Jack Russell is a werewolf, the son of a Transylvanian nobleman and baron. One descended from a family which had been cursed by Chthon an Old One. It was the curse of lycanthropy which remained dormant until his father activated it by reading a passage in the Darkhold. On his 18th birthday, he turned into a werewolf.
Ever since he has been trying to find a cure (and for his sister who also became a werewolf though she was later cured by a sorcerer who took the curse upon himself) and until then ways to control or minimize the curse. An adventurer who lives off the trust fund established by his mother through the sale of his father's estate, he has fought the evil forces of the supernatural both individually and as a member of the Midnight Sons. Which has included the Cult of the Darkhold and the Wolf Lord Varcolac.