The Diablo Universe involves angels, demons, super humans, giant spiders, world-bearing dragons, an earth that shouldn't rightly exist, necromancy, shape shifting druids, maddened kings, and warring nations: getting lost in it can be easy. This article sums up the very basics of events in chronological order, starting from the very birth of reality and ending with what is known for fact. It also aims to summarize the most important facts that we know of regarding the backstory that will set the base for Diablo III.
SPOILER ALERT: While all articles in this wiki are prone to spoilers, this page will reveal basically all plots and story elements of all games and books released to date. It is therefore probably safe to say that it is the most spoiler-intensive article in the wiki. If you do not wish to have your reading or playing experience spoiled, do not read this article.
 The Beginning of the Great Conflict
Since the birth of reality itself, the high Heavens and the pits of Hell have waged an endless war for anything of value within their realms of order and chaos. No side has gained much of anything at all for long, and, in their struggle, have often destroyed much of what they sought to claim. It is referred to as The Great Conflict, and all other wars and events, like The Sin War, fall under it.
The story begins with Inarius, a powerful angel and member of the Angiris Council. Tired of the constant fighting, he sees little point in their infinite war they are waging against Hell. Convinced that there must be others such as him in both Heaven and Hell, Inarius starts to search for other individuals who share his views on the war. To his surprise there are many such as himself, and together with Lilith, daughter of Mephisto, he leads a great exodus. Together, they defect from Heaven and Hell and search for another place to live. They succeed in stealing the Worldstone, and perform two tasks which above all others will affect the course of history:
- Create Sanctuary, the world of men, as a paradise and refuge from the Great Conflict
- Create the Nephalem, the first humans
To protect this world from both Heaven and Hell, they used the stolen Worldstone. It acted as a protective barrier, and effectively prevented angels and demons from either directly invading Sanctuary or noticing its existence at all. How exactly it worked remains unclear, but work it did.
The two races of Heaven and Hell tried to live peacefully with each other on Sanctuary, and even mated with each other, spawning the first generation of humans, called the Nephalem. It quickly became apparent that the Nephalem were as powerful as their parents, and had the potential to be much, much more than any angel or demon. This caused struggle among the higher beings. Inarius wanted to kill the humans, as he viewed them as a threat to their own existence. Lilith, on the other hand, wanted to raise the Nephalem to an army and have them fight both Heaven and Hell. The two began fighting, and Inarius cast out Lilith from Sanctuary and imprisoned her in The Void, claiming Sanctuary as his own. Many of the Nephalem were slain during this time, but some survived, like Bul-Kathos and Rathma. The latter became the servant of Trag'Oul, a mystical dragon, and guardian of Sanctuary.
 The Sin War
- This section deals largely with information from The Sin War Trilogy
- "All praises to Diablo - Lord of Terror and survivor of the Dark Exile. When he awakened from his long slumber, my Lord and master spoke to me of secrets that few mortals know. He told me the kingdoms of the High Heavens and the Pits of the Burning Hells engage in an eternal war. He revealed the powers that have brought this discord to the realms of man. My Lord has named the battle for this world and all who exist here the Sin War."
As time went on, the Prime Evils discovered Sanctuary. Immediately realizing the potential of humanity as a weapon against Heaven, they created a religion called The Triune there to lure humans to their side. Inarius thus similarly set up his own Cathedral of Light to combat the Three. The two forces battled behind the scenes with each other on Sanctuary, while Heaven remained unknowing of Sanctuary's existence. The two religions waged a constant but seemingly petty war against each other, and the world was more or less unaffected. The two churches meddled in the everyday lives of humans sometimes, but none except for the most high-ranking of the church servants knew the true identities between the religions. That all changed when Lilith broke free of her prison. Returning to Sanctuary, she once again sought to use the humans to her own advantage and conquer both Heaven and Hell.
In these events, a man named Uldyssian, a distant descendant of Inarius and Lilith, got caught in her plots. Unbeknownst to him, Lilith gave him magical powers and framed him. Making it appear as though he had slain the servants of both the Triune, and the Cathedral of Light. Lilith disguised herself as a human named Lylia, and snared Uldyssian into doing as she wished. Uldyssian thought that these powers lay latent in all humans, and, followed by Mendeln, his younger brother, Serenthia, a longtime family friend infatuated with Uldyssian and the daughter of the merchant Cyrus, and Achilios, a childhood friend and archer, fled the town of Seram fearing for their lives. The very people who were once close friends and neighbors turned upon Uldyssian fearing his new abilities, and what it seemed that he did with them. Uldyssian blamed the Triune, and the Cathedral for the predicament he was in and so set off to awaken these powers in others, that they might live in a world of their own crafting, not the Triune or Cathedral. The venture was a struggle at first, but with the unknown aid from Lilith, more and more people were found who could use magic, and they gathered under Uldyssian. They became known as the Edyrem, with Uldyssian as their leader.
These actions brought with them turmoil. Lucion, leader of the Triune and son of Mephisto, sent formidable enemies to hunt down Uldyssian, among them Malic, Damos, Gulag and Astrogha (the latter who also appears in other novels, most notably Moon of the Spider).
Mendeln, during this time, was noticed by Rathma. Rathma was the son of Inarius and Lilith, and the first servant of Trag'Oul, a great dragon connected to Sanctuary but aligned with neither Heaven nor Hell. Rathma trained Mendeln as an apprentice, and they are the first two Necromancers.
Lilith in the meantime understood that her plans could not be achieved unless something was done with the Worldstone. The crystal had been created by Inarius to both shield the world and to limit the powers of humans. So long as it still stood, no human army of hers would ever wage war with Heaven or Hell. Uldyssian however was brought there, and after a brief brawl with Bul'Kathos, he was allowed into the Worldstone Chamber with Rathma as his companion. After killing bat-like demons Rathma, though doubtful he would succeed, suggested Uldyssian attempt to change the worldstone to better favor him and his people. What he did astonished Rathma, and later Inarius as well. Uldyssian had altered the structure of the crystal, something not even Inarius could undo. This change had monumental consequences, and not only stopped the weakening of the Nephalem, but in fact sped up the growth of their powers.
Eventually Inarius was dragged into the conflict. The tyrant ruler of Sanctuary, he had considered himself above Uldyssian and refused to come into direct contact with him. Because of that belief, he sent his trusted assistant Gamuel to assassinate Uldyssian. The plot failed and Inarius resorted to even more desperate measures, a pact with Diablo himself. At this point, the human's powers had grown immensely, and a confrontation was imminent. Initially Inarius did not view Uldyssian as much of a threat, but as his efforts to stop the human continued to fail, Inarius became more and more desperate (though he refused to admit as much to himself). At this time, Inarius was approached by Diablo, and the Prime Evil offered him a pact. Together the two sought to defeat Uldyssian and his Edyrem. At the same time, Tyrael discovered Sanctuary, and soon thereafter the High Heavens was notified of the existence of this world.
The High Heavens viewed Sanctuary and its inhabitants as an abomination to existence, and acted accordingly, sending their armies directly to Sanctuary. Trag'Oul, the guardian of Sanctuary, used his immense power to shield Sanctuary's location from the angels but he could not hold it forever. Uldyssian and Inarius also clashed, and that battle is without a doubt the fiercest battle that has ever taken place on the face of Sanctuary, and likely ever will. Both wielded the strength of gods, and continually changed the landscape surrounding them as they battled. As they fought, a tear appeared in the sky as the hosts of angels finally reached and invaded Sanctuary. Soon after, Uldyssian's entire body infused with energy, he acquired a higher understanding of Sanctuary itself and easily broke the bond between Inarius and the Worldstone. Inarius, without the immense amount of power to draw upon was easily defeated by Uldyssian, and trapped in a prison until the Angiris Council further decided his fate. Soon after the angels reached Sanctuary, Tyrael found Uldyssian and shackled him. Demons of the Burning Hells, determined not to let the angels destroy what they sought to exploit, erupted onto the landscape and a three way battle commenced. The angels battling on one side, the demons on the other, and the Edyrem stuck in the middle. Uldyssian still shackled, was forced to watch his people as they fought against both angel and demon. Overcome with emotion, he finally broke free of Tyrael's bonds and demanded the armies to stop. Surprisingly, they all became frozen in time. Uldyssian then cleared the angels and the demons from his world. He began changing the landscape back to how it was before all the destruction had taken place. As he did so, his powers refused to cooperate and instead destroyed the environment where he was trying to fix it. He realized the only thing he could do was to draw the destruction into himself, and so with all his might he did so. Finally, after taking in all the destruction that Sanctuary had suffered, Trag'Oul guided him to The Void to release it:
He felt the pressure building up again--this time for the final moment--and readied himself and his world for it.
And when it came, it did so with an explosion of pure energy that ever so briefly shook Sanctuary to its foundations. Uldyssian roared, not because of pain but rather the sheer ecstasy of his transformation. He was no longer a mere human but something of which even the angels and demons could not conceive. He was Sanctuary for one moment, and all that surrounded it. His presence dwarfed that of Trag'Oul... of any being near. His consciousness spread out above his treasured world, where he looked at it one last time.
 The Reset
After the battle, a gathering was held between the Angiris Council and Mephisto. Sanctuary was all but destroyed, but all hope was not lost. Some, like Rathma, pleaded with Heaven to spare Sanctuary. A vote was held between the Angels. Imperius voted against Sanctuary's existence and Auriel argued strongly for it. The deciding vote was laid by Tyrael, who initially seemed to show little love for humanity, something which has evidently developed over the years since this event. Together with Mephisto, a deal was made between Heaven and Hell. Sanctuary was to live on its own, with no war brought there by Heaven or Hell. Humanity would choose for themselves what to do. In return for agreeing to this, Mephisto obtained custody of Inarius and took him to the Burning Hells. Why Mephisto sought Inarius is unknown.
This was followed by a reset of the world. Time was reverted right to the point where Uldyssian left his home village, and events were unmade so that the inhabitants of Sanctuary could mature on their own, without the influence of the Triune, or the Cathedral.
- All memories were wiped save that of the original Nephalem (the reasoning was that the original Nephalem were very few and they would pass-on soon enough anyway) and Mendeln (Trag'Oul saved him his memory so he could remember the sacrifice his brother made, as well as teach any willing students the ways of the balance).
- Serenthia is revived and Achilios is turned back into a living human because of Uldyssian sacrificing himself (this is a direct effect of Uldyssian's sacrifice, has nothing to do with the Angiris Council or Mephisto)
- The Cathedral and Triune were no more.
This, the reset world, is the past from which the games take place. The first 'version', with Uldyssian, isn't recorded in any history but is known by a few humans, as well as angels and demons naturally.
 The Dark Exile
- "So it came to be that there was a great revolution within the Burning Hells known as the Dark Exile. The Lesser Evils overthrew the three Prime Evils and banished their spirit forms to the mortal realm. The Demons Belial (the Lord of Lies) and Azmodan (the Lord of Sin) fought to claim rulership of Hell during the abscence of the Three Brothers. All of Hell polarized between the factions of Belial and Azmodan while the forces of the High Heavens continually battered upon the very gates of Hell."
Azmodan, Belial, Andariel, and Duriel are the four Lesser Evils of Hell. Whether Diablo and his brothers intended for it or not, the Four Lesser Evils plotted and ultimately exiled the Three Primes into Sanctuary. In their absence, Belial, the lord of Lies, and Azmodan, the Lord of Sin, engaged in a civil war between themselves. Their war rages in the deepest pits of Hell to this day.
 The Horadrim
Tyrael learns of the Three's exile into Sanctuary and mobilizes to stop them. He creates the Horadrim, a collection of the most powerful human Magi, including Jered Cain, Deckard Cain's ancestor, and Tal Rasha. Tyrael charges the Horadrim with the capture of the Three Prime Evils, giving them Soulstones to imprison the souls of Diablo and his brothers within. One by one they find and imprison the Primes. Unable to permanently destroy the demons, the Horadrim are forced to instead hide the Soulstones. Their locations are as follows:
- Baal’s Soulstone was imprisoned inside a huge tomb constructed with a single purpose: keep him in and others out. Baal had damaged his soulstone during his capture due to his destructive nature. Tal Rasha, knowing that the final shard of Baal's broken Soulstone was not great enough to contain the Prime Evil, chose to use his own body as a prison for the Prime. Lodging it into his chest and binding himself to a pillar, Tal Rasha remained in the tomb for centuries, containing the Evil within.
- Mephisto’s Soulstone was sealed inside a temple in Kurast, although he had originally been captured in Aranoch along with Baal. Afraid to imprison two Primes so close to each other, the Horadrim chose to move him. The Zakarum monks were tasked with its protection (ultimately, however, the Soulstone corrupted the monks and Mephisto took a host among them).
- Diablo had fled to the west and continued to evade capture for several decades after his brothers' capture. Eventually he was captured near today's Westmarch, and the Horadrim built a cathedral above his tomb to stand guard. As time passed by however, the Horadrim fell apart, and no one else remembered the evil imprisoned within.
 Diablo 1
- "Hail and sacrifice to Diablo - Lord of Terror and destroyer of souls. When I awoke my master from his sleep, he attempted to possess a mortal's form. Diablo attempted to claim the body of King Leoric, but my master was too weak from his imprisonment. My Lord required a simple and innocent anchor to this world, and so found the boy Albrecht to be perfect for the task. While the good King Leoric was left maddened by Diablo's unsuccessful possession, I kidnapped his son Albrecht and brought him before my master. I now await be rewarded when he at last emerges as the lord of this world."
 King Leoric
A conquering hero known as Leoric established himself as the king of Khanduras, a kingdom on the Western continent of Sanctuary. He appointed Tristram as the capital of this kingdom and used the abandoned cathedral there as his throne and central point of governance. Not soon after, King Leoric's most trusted advisor Archbishop Lazarus was drawn deeper into the cathedral by the Lord of Terror's Soulstone. The Archbishop, whether out of fear or temptation, shattered the Soulstone, releasing Diablo's trapped spirit. Unable to take King Leoric himself as a physical host, Diablo had the Archbishop Lazarus kidnap the king's son, Prince Albrecht, and brought him down into the Cathedral for Diablo to corrupt and use as his host to fully manifest as the Lord of Terror.
The King, already deranged from Diablo's attempts to possess him, went mad in his search for his lost son, sending many to their death out of suspicion of guilt. Ultimately Lazarus led the town's warriors into the cathedral as a trap for The Butcher, a minion wielding a bloody cleaver. King Leoric's physical form had withered away, but his soul found no peace and returned as a giant skeleton, still wearing his golden crown.
 Tristram's Hero
Several heroes travelled to Tristram, hearing rumors of a corrupting evil, vast riches, and arcane magic. The heroes were assisted in their journeys by Deckard Cain, a descendant of one of The Horadrim. Canonically, it was Aidan, the playable Warrior character and the son of Leoric, who sought and ultimately vanquished Diablo. Thinking he was able to contend with its evil, Aidan forced Diablo’s Soulstone into his own forehead. After returning to Tristram, the town's inhabitants celebrated their champion's victory, but Aidan had returned a much changed man, haunted by Diablo's essence.
Aidan departed Tristram and travelled to the East for answers to his nightmares.
 Diablo II
The vanquisher of Diablo finds himself taking refuge in a tavern from the blizzard. Perhaps stirred by the other drunk men, or perhaps simply unable to contain the Lord of Terror within himself any longer, the tormented champion suddenly erupts into chaos. Demons and skeletons spawn and slay all within the tavern, but one: Marius, a human bystander whom the Wanderer urges to follow him for unknown reasons.
 Act I - The Rogue Encampment
The champion becomes The Dark Wanderer, and begins to journey onwards towards the Rogue Monastery. Once there, he drives the Sisters of the Sightless Eye out of their monastery, and tasks Andariel with the guarding of the pass from anyone who might follow.
As did heroes arrive in Tristram to find adventure, glory, or riches, more arrive in the Rogue Encampment for similar reasons. A band of adventurers form and seek the Monastery and the evils that lie within. From an overrun Tristram, they rescue Deckard Cain, who guides them on their way to the Monastery, where they defeat Andariel and find clear passage to Lut Gholein.
 Act II - Lut Gholein
With Marius, The Wanderer travels East to Lut Gholein to search for the Tomb of Tal Rasha and finds Tal Rasha still imprisoned in the final chamber. Tyrael, however, having discovered The Wanderer's escape from Tristram, is there waiting for him. Tyrael and a now empowered Wanderer lock into combat. Baal, still trapped in Tal Rasha's body, notices that Marius is also present, and though the Prime Evil has deformed his host greatly in the years of imprisonment, he is powerful enough to trick Marius into seeing him as nothing but a chained human. He lures Marius into pulling the soulstone from Tal Rasha's chest, destroying Baal's prison. Baal and his brother Diablo overwhelm Tyrael and trap him in the tomb, summoning Duriel to prevent the Archangel from following. Tyrael, with no chance of pursuing, tasks Marius with taking Baal's Soulstone and traveling to the Eastern kingdom of Kurast. There, the Archangel commands, Marius must enter the portal into Hell and destroy the Soulstone at the Hellforge.
The band of heroes who had slain Andariel at the Monastery now seek the Tomb of Tal Rasha, where Baal, the Lord of Destruction, is said to be kept imprisoned. With the help of Cain, the Horadric Cube, and Lut Gholein's inhabitants, the adventurers ultimately find their way to the Arcane Sanctuary. There in that twisted reality they find The Summoner, the entrance to the Canyon of the Magi and finally Tal Rasha's Tomb. Having found the true tomb, the party defeats Duriel and frees Tyrael.
Now forced to pursue The Dark Wanderer and Baal, the heroes sail East to Kurast, city of the Zakarum.
 Act III - Kurast
The Dark Wanderer, whose growing corruption by Diablo's spirit continues to pervert his form, and Baal proceed to free their eldest brother Mephisto in Kurast. The last imprisoned Prime Evil was once given to the care of the Zakarum church, but was able to corrupt the entire faith from within his soulstone, and all but their highest leader, Khalim, the Que-Haegan, fell to his influence. The High Council, which had previously led the order of the Paladins, became the arm of Mephisto in Sanctuary. Thus the two evils have little trouble reaching their brother once they reach Kurast. Once again united, The Dark Wanderer takes a new form as the Lord of Terror, Diablo, and the Three open up a portal to Hell. Diablo is tasked with reclaiming Hell for their use, presumably from the warring Azmodan and Belial. Diablo steps through to the portal and into Hell.
Oblivious to the Three, Marius has witnessed their meeting and his companion's transformation. Although charged by Tyrael to venture into Hell, he does not find the courage to do as the Archangel instructed. Instead, he retreats and finds bastion in a mental asylum.
Baal likely follows Diablo shortly afterwards, for when the player reaches the lowest level of Mephisto's Durance, Baal is not there. The Three must be aware of the heroes pursuing them by now, for Mephisto has stayed behind to stop them. He is, however, defeated by the venturing band of heroes. His Soulstone remains intact, and it is taken through the portal to Hell.
 Act IV - The Pandemonium Fortress
In Hell, the heroes find themselves operating out of the Pandemonium Fortress, which is the foremost bastion of Heaven in their war against Hell. From here, the heroes are instructed to carry out three important missions:
- Seek Izual, the fallen angel, and slay him for his betrayal.
- Seek the Hellforge and shatter Mephisto's Soulstone.
- Seek Diablo in his sanctuary and vanquish him from the mortal realm.
Izual at one point was one of Tyrael's most celebrated lieutenants. Untill, going against the wishes of the Angirus Council, he led an ill-fated assault upon the Hellforge. Attempting to stop the creation of Shadowfang, an evil weapon being created to combat the Azurewrath, the blade carried by Izual himself. During the assault, he was captured and tortured for information. He gave in and spilled secrets of The Heavens to the armies of Hell. Upon his return from the pits of Hell, the Angirus Council, angered by his disobedience and engraged by his betrayal, punished him by locking his form within a demon from the abyss and banished him to The Void. Tyrael gives this quest, and asks that Izual be put out of his misery. Originally he then appears to be a miserable character, but upon his death, Izual tells the band of adventurers that he told the Prime Evils how to corrupt the soulstones and so helped them "mastermind their own exile" into Sanctuary. In truth then, Izual appears to have played a crucial part in the plot, and without him it is unlikely the Dark Exile would ever have taken place.
After having slain Izual and shattered Mephisto's Soulstone, the heroes move towards Diablo. The Lord of Terror fortifies himself in the Chaos Sanctuary. Its architecture is towering and gothic, but its purpose is unknown. The band of heroes defeat Diablo and his soulstone is smashed at the Hellforge.
Diablo now defeated, Baal seeks out Marius and finds him in the asylum. Disguised as Tyrael, Baal requests Marius cede the Soulstone to him. He does, only to realize his grievous mistake moments later. Baal kills Marius and burns down the asylum. The failure of Marius does not bode well for Sanctuary.
 Diablo II: Lord of Destruction
 Act V - Harrogath
In the expansion pack, Baal, the last living Prime Evil, returns. Fortunately for Baal, he was imprisoned in Tal Rasha, and the great Horadrim mage was one of the few who knew the exact location of the Worldstone, the barrier hiding Sanctuary from other worlds. With the location revealed to him as Mt. Arreat, he launches an all-out assault upon it.
His assault on Mt. Arreat and the Barbarians living there is a success. The human forces are overwhelmed by Hell, and in the end only one city, Harrogath, still stands. All but one of the town's elders - Nihlathak - sacrificed themselves to raise a ward to block out all demons. Regardless, Baal is not impeded by this last town, and moves on toward Mt. Arreat. It is to this town that the heroes arrive, and from there they fight their way forward in Baal's tracks.
Atop Mt. Arreat lies the last protection of the Worldstone: three barbarian heroes; Korlic, Madawc and Talic, who were once selected by some Nephalem (most likely Bul-Kathos with some others) to stand guard over Mt. Arreat and protect it from any who tried to enter without carrying the Relic of the Ancients. This relic was in the possession of the elders of Harrogath, and since they all died, it was left to Nihlathak. Knowing this, Baal traded Nihlathak this relic for an assurance of Harrogath's safety. Once in possession of the relic, he was able to freely pass the Ancients.
The heroes, not having the relic themselves, were therefore required to face the Ancients as they followed Baal. Even though the Ancients should likely aid humanity, and even speak against Baal and his actions, still they fought with the heroes, but were defeated and allowed the humans to pass into the Worldstone Keep. Within, Baal is found and killed, but not before he reaches the Worldstone and taints it. Tyrael appears next to the Worldstone and grants the heroes safe passage back to Harrogath, but must himself contend with the predicament of the corrupted Worldstone. Without any other option to save humanity, he hurls his flaming sword into the Worldstone and shatters it into an infinite number of pieces, its destruction appearing as if Tyrael had thrown a boulder into a lake of water but the splashes and ripples were manifested as shards of crystal.
This is the end of Diablo 2: Lord of Destruction, and the destruction of the Worldstone occurs twenty years prior to the events in Diablo III.
Knowledge of the Diablo world is accessed from the following sources:
- Diablo I, the first game released in 1997
- Diablo II, the second game released in 2000
- Diablo II: Lord of Destruction, the expansion to the second game, released in 2001
- Demonsbane, an e-book written by Robert B. Marks, the first set in the Diablo Universe.
- Legacy of Blood, a book written by Richard A. Knaak
- The Black Road, a book written by Mel Odom
- The Kingdom of Shadow, a book written by Richard A. Knaak
- Moon of the Spider, a book written by Richard A. Knaak
- The Sin War Trilogy, written by Richard A. Knaak, consisting of:
All of these works are considered canon, and if any works contradict each other, then the newest work takes precedence. For example, much of what is outlined in the Sin War trilogy contradicts what we know of from the games, however the books have been written in collaboration with Blizzard and are considered official, and since they are of a later date, they are to be considered correct.
Important to note is that
- Diablo: Hellfire is not official canon. It was developed by Sierra, a sister company to Blizzard Entertainment under Vivendi, and while Blizzard may draw inspiration from it, none of it is to be considered official canon.
- The Veiled Prophet, page 325. Richard A. Knaak, 2007.