Felix Blackthorn is the father of Annabel Blackthorn.
Felix and their family eventually found out that his daughter, Annabel, had become romantically involved with Malcolm and ran away with him, taking the Black Volume with them. They were caught by the Clave, and Annabel was tortured for information on Malcolm and the book before being returned to them, for farewells before Annabel's departure for the Adamant Citadel to become an Iron Sister. He was disgusted with her association with Malcolm and, conspiring with some members of their family, had her buried alive.
When Inquisitor Dearborn came looking for Annabel, Felix, anticipating the summons, came with his friends, including a Herondale, and family as backup. The group was able to convince the Inquisitor to cover up Annabel's absence and pass her off as an Iron Sister to the rest of the Shadow society.
Felix is a very cold man and believed Downworlders were filth. His hatred is so great that he disowned his daughter after she fell in love with a warlock, and buried her alive as she had disgraced her family in his eyes. Felix is able to stay calm under pressure, as he maintained a composed appearance when being questioned by the Inquisitor.
Felix has brown hair streaked with gray and a broad face which bore the marks of a bad temper.
- Lord of Shadows (first and only appearance) (appeared in projected memories)