Louis was the husband of Lenore St. Croix, they were married in 1947. They were on their way back from the honeymoon, eager to start their new life together, but they had a car accident with a drunk driver. The shock of the accident triggered Lenore's mutant power. Louis tried to save her, but she died en route to the hospital, after the paramedic that came to help refused to touch her due to his mutant power.
Years later he apparently married another woman who bore him a son, Cartier St. Croix.
- In X-Factor #200, in Monet's entry says that Louis St. Croix and Cartier St. Croix are two different characters.