Leon

Leon
Leon, is a powerful angel of the Lord, who was responsible for saving Celan from Hell, on the archangels' command. It was his job to help prevent Lucifer from breaking the 666 law that, once broken, would release Lucifer from his cage. Once Leon learned that the angels wished to free Lucifer anyway, he defied his angelic brethren and died trying to help Celan prevent Mike Williams from breaking the last law 

After he was killed by Raphael, Leon was resurrected by God and joined Mike, Celan and Ruby in a quest to stop both Heaven and Hell to prevent the brothers from becoming the vessels of Michael and Lucifer. When the Apocalypse was averted, he was again resurrected with new powers, being promoted to Seraph. He then started a civil war in Heaven to prevent Raphael from restarting the Apocalypse. Thinking he could not be outsmarted by a demon, Leon teamed up with Crow to claim the souls of Death Hell. He ended up betraying Crow and absorbed all the souls, resulting in his powers reaching the level that of a god, but at a high price: the powers that the evil souls granted him had warped Leon's mind, causing him to proclaim himself as the new God.

Leon later agreed on the advice for Celan to release the souls back into Death Hell. While seemingly successful, it turned out that the most powerful entities from Death Hell held on to Leon, and overpowered and took control of him. When the Leviathan leave to take over new form, Leon was presumed dead, but survived - apparently resurrected by God yet again. Celan later accidentally finds Leon as an amnesiac healer called Emmanuel. After taking on Mike's madness and experience in Hell in order to save the Heroes and redeem himself for what he did to Mike, Leon had become insane and fell into a coma. However, he awakens and his sanity is returned to an extent when a signal was sent to all angels upon the discovery of the Word of God and the appointment of a new prophet.

While Celan returns, Leon is not with him. While his condition is initially unknown, it's revealed that he spent most of his time running from Leviathan and that he didn't escape Death Hell with Celan as he had planned to stay as a form of penance. However, he was eventually released from the monster realm by an incursion of angels under the orders of a mysterious but powerful angel named Naomi.

After being stripped of his grace by Gabriel in order to expel all angels from Heaven, Leon spends the next three months on Earth as a human. After being captured and tortured by an angel named Malachi, Leon steals the grace of Theon and returns to his former status as an angel (previously being promoted to a Seraph).