Theo Mikaelson

Theo Mikaelson is the firstborn son of Gabriel Mikaelson and Josette Saltzman. He is the older brother of Damian, Finn, Andreas, and Evelyn Mikaelson, and is the paternal grandson of Hayley Marshall and Niklaus Mikaelson. His biological maternal grandparents are Alaric Saltzman and Josette Loughlin. He is also the surrogate grandson of Caroline Forbes and the step-grandson of Stefan Salvatore. He is the maternal nephew of Elizabeth Saltzman and the paternal half-nephew of the reincarnated Thomas Shepard and William Kaplan. By virtue of his father's heritage, he is the adoptive nephew of Marcel Gerard.

Like their father, he and his siblings are natural-born Tribrids, though they are far less powerful. His mother was a Heretic, a Vampire-Witch who was originally a Siphoner of the Gemini Coven. He gets his vampire and witch legacy from both his parents, but also has a werewolf gene due to his paternal lineage. Technically speaking, he is three eighths witch, three eighths vampire, and one eighth werewolf, whilst his father is half-werewolf, quarter witch, and quarter vampire, in terms of genetics.