Rathma is a nephalem and the first necromancer. He is the son of Lilith and Inarius. His birthname was Linarian, which he came to reject and instead he embraced his current name, Rathma, given to him by Trag'Oul. It means "Student" and refers to his relationship with Trag'Oul, who taught him about the Balance and the way of the necromancer.
It is unknown whether he still lives, but if he does so he is one of the last remaining nephalem, perhaps even the only one.
During the events of the Sin War Rathma works together with Trag'Oul to make sure that Heaven remains oblivious to the existence of Sanctuary, and to try and limit Hell's influence as much as possible. The two work alone for quite some time until they notice the ul-Diomed brothers Uldyssian and Mendeln, who both become pivotal in the shaping of Sanctuary's future. Mendeln, they realize, has a great potential for helping them maintain the Balance, and Rathma begins to test and evaluate Mendeln without him being aware. Rathma eventually confronts Mendeln directly, and though the young man remains skeptical at first, he eventually joins forces with Rathma and Trag'Oul and becomes the second necromancer ever.
In addition, Rathma plays several other key roles during the Sin War. He aids Uldyssian, Mendeln's elder brother, on a number of occasions. The most important of those is arguably the time when Rathma teleports them to the Worldstone, at which time Uldyssian makes his alteration to the stone which will ultimately lead to a great rise on power among the edyrem. Rathma also tries to negotiate with his father to cease hostilities with Uldyssian and instead focus his attention on Heaven and Hell, and although the attempt fails he also rallies the remaining living nephalem for the final confrontation between Inarius and Uldyssian on the Grasslands.
He is described as having "too perfect features, a trait present in all nephalem. His skin is a pale white and his hair is black.
In addiion, he wears a rather peculiar cloak. It shifts and moves in repsonse to is emotional state. Mendeln theorizes that the cloak might be alive, but he does not actually inquire about it.
Rathma is a very calm and rational man. He is not cold or uncaring, but he rarely displays emotion and thus comes off as such. Because of this, his initial interactions with both Uldyssian and Mendeln are problematic. Both brothers are wary of him at first, and though Mendeln eventually comes to trust him and befriend him, Uldyssian never manages the same feat. Other characters remain skeptical towards him as well.
He is not at all in good terms with his parents, as Lilith destroyed the rebel angels and demons to try and force Inarius to let her use the nephalem's power for her own ends.
In addition to the powers necromancers possess such as raising and communicating with the dead, unleashing Teeth and Bone Spear among other things, he is also shown to have two other distinctive powers. The first is his ability to teleport over great distances across Sanctuary and to Trag'Oul's Realm. This power might stem from his close ties to Trag'Oul. The second is his ability to read sensations of people, which is similar to reading thoughts. It is unclear where these powers comes from.