As a child, Victor lived in America with his parents. After he unsuccessfully brought his dog back to life, he and the dog's corpse instead fell into a portal though space and time to the Victorian era in England, where he was adopted by a fish monger and his wife. Because of the trauma of the jump, the death of his pet, and his adopted parents insisting it wasn't real, he mostly forgot about his old life, and built for himself a new one.
After his ordeal with death for the second time, with Emily, he was shaken, and glimpsed memories of his life in the future came to his mind, but Victoria helped him move on. When she and their first daughter died in childbirth, he spent the evening after the funeral drowning his sorrows in cheap scotch. In his drunken state, he threw a bottle into the fireplace. The resulting flare from the alcohol caught the edge of his coat, because of his close proximity to the flames, and he was burned to death, along with the house.
Because of the pain he endured in life, his soul was sent to Halloween town, to govern the holiday which celebrates fear, being given the physical form of his body after the flames had killed him, bones burned clean of flesh, which became white after cleaning himself, as well as the name Jack. Because he was dead, he had almost no memories of his life in England, and only vague feelings of his life in future America. He was reunited for the second time with his childhood dog and renamed him Zero.
When he encountered Christmastown, he remembered joy in life, and attempted to regain that feeling. Calling back on the residual memories of science from his human life, he recreated a twisted version of the holiday. After his self discovery after being shot from the sky and saving the lives of Sally and Santa, he regained a sort of calmness, or rather a gentle morbidity rather than the frenzy he had worked himself into while taking over Christmas. And so the man born Victor who grew to be Jack was finally free, and no longer was he alone.
La Fin.