Felix Blackthorn was the father of Annabel Blackthorn.
In the 1800s Felix took in a young warlock named Malcolm Fade, and gave him his family name, Blackthorn. When Felix' daughter Annabel fell in love with Malcolm and tried to run away with him and the Black Volume of the Dead, Felix found out and reported his daughter to the Clave. She was tortured for information and released back to him to say goodbye before being sent to the Adamant Citadel; disgusted with her association with Malcolm, Felix buried her alive in a tomb by the sea rather than let her become an Iron Sister. When Inquisitor Dearborn came looking for Annabel, Felix, anticipating this, summoned his friends and family and told the Inquisitor he was not hiding her, as she was no longer part of his family. After one of his friends, a Herondale, offered a solution for the situation, Felix was visibly relieved when the Inquisitor agreed not to ask any more questions.
Felix was a very cold man and believed Downworlders were filth. His hatred was 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 was able to stay calm under pressure, as he maintained a composed appearance when being questioned by the Inquisitor.
Felix had brown hair streaked with gray and a broad face which bore the marks of a bad temper.
- Lord of Shadows (flashback)