The Mystic Falls Codex

Born to an enslaved woman and the man who owned her, taken in by Klaus as a boy and named Marcellus — "the little warrior." Klaus raised him, taught him everything, and turned him. Rebekah loved him. In 1919 Mikael came, Klaus fled, and Marcel was left for dead. He was not dead. He took New Orleans instead and ruled it for ninety years, keeping the witches suppressed by hiding a teenage witch named Davina Claire and using her power against her own covens.

Half of The Originals is a custody fight between two men who each believe they made the city and each believe they made the other. He eventually takes Lucien's serum and becomes the Beast of the prophecy — an upgraded Original whose bite can kill a Mikaelson without white oak.