The main 'hero' in the story, insofar as any of the characters can be called heroes. Ivan originally started out as a mortal Christian priest.
However, because of an essay he wrote while training to become a priest he came to the attention of a special branch of the Roman Catholic Church. This branch then approached him after he had become a priest to help unlock the secrets of an artifact called the Domas Porada, a prison which contains Temozarela, and Belial, who sealed himself in there in a battle with Temozarela.
Temozarela, realizing that Ivan could break him out of the prison, caused the death of his adopted sister/lover, Gena, knowing this would make Ivan temporarily insane through grief. Ivan, in his insane state, breaks Temozarela free and is in turn trapped within the Domas Porada in the fallen angel's place.
Ivan, realizing what he has done, agrees to give half his soul to Belial in exchange for a chance to get revenge on Temozarela and his fallen angel brethren. Ivan now stalks the west as an undead creature sustained solely by his infinite rage. Indeed in numerous encounters it is shown that his strength is directly related to his anger. Where his inhuman strength fails, he uses a variety of weapons, including a bowie knife he coats with blessed silver and silver bullets in a sawed-off shotgun, and a Thompson sub-machine gun (one of many anachronistic firearms in the series).
Ivan then embarks on a quest to destroy the thirteen angels. He successfully defeats countless minions and also slays Jarbilong, being defeated himself by Achmode who devoured Ivan's right arm. Ivan is given Achmode's blasted arm after he is punished with death by Armand, a fellow - yet much stronger - Fallen Angel.
As he continues to make his way across the west, he finally comes to fight Armand himself, only to be dealt a debilitating wound on his heart, which saps his rage and emotion from him. This is a near fatal blow for both Ivan and Belial, who depend on Ivan's unquenchable rage to keep up his supernatural powers. Netraphim comes to him and heals him as best she could, but unable to stop the bleeding completely. It is only with her last words to him that Ivan is able to gain the will to fight once more, his rage at full force once more.