The adventures of Achilios began when he discovered a mysterious object in the woods. When he touched the object, he felt an emptiness akin to death.
Malic, as a member of the Triune, laid a curse on Achilios' bow that it might always miss its target. Despite this, Achilios' great skill allowed him to overcome the magic. This did not save him from being killed by his own arrow whilst fighting Lucion (Diablo)Lucion. He was buried in the wilderness.
At some point, Rathma resurrected Achilios as an undead being with the hopes that he would continue to assist Mendeln and the rest of his friends against the Triune and Lilith. While involved in this quest, Achilios fought off Triune assassins and helped expel Lilith from Serenthia's body.
Afterwards, Tyrael imbues Achilios with holy power, which forces Achilios to obey the angels instead of Rathma. He was commanded to kill his allies, but Achilios' love for Serenthia and strong will allowed him to overcome this order and aid his friends at the Battle of the Golden Path.
When Uldyssian sacrificed himself, Achilios was restored to life.
Achilios is a character seen in most of the Sin War Trilogy.