Desiderius was the son of Bacchus and an Apollite woman. His father wouldn't help him escape the Apollite curse, so he turned Daimon. His demigod status made him faster and stronger than other Daimons, so he survived for about 250 years.
His downfall came in Night Pleasures when he handcuffed Amanda Devereaux to Kyrian of Thrace, hoping she would unleash her suppressed psychic powers and kill Kyrian. He released them and they fell in love with each other by the time he recaptured them. She used her newly unlocked powers to help Kyrian kill Desiderius.
In Seize the Night, he was reincarnated by Stryker in exchange for wounding Acheron Parthenopaeus. Although he had regained his own body, he possessed the Dark-Hunter Ulric in order to get closer to his victims. In Ulric's body, he murdered Tia Devereaux, Cherise Gautier, Amanda Devereaux, Kyrian of Thrace, and the Dark-Hunter Kassim before Tabitha stabbed him in the heart and Valerius beheaded him.