Papa Jupiter was born a monster. He was the son of a hillbilly named Fred, who realized how evil Jupiter was when he killed his sister, and he killed all the animals on his farm. Fred took Jupiter to the hills after his daughter's death and he tried killing Jupiter with an iron, but it failed.
Papa Jupiter got with a prostitute who was insane, and he had children with her, mutant offspring who were insane and cannibalistic. In the remakes, the gang is the result of government atomic testing in the desert.
Papa Jupiter is unseen for most of the film, but his presence is enough to scare the most hardened of the mutants in his gang. Papa Jupiter is very intimidating, and he is first seen when Fred asks Ruby, one of the mutants, if Jupiter knows about what she's doing because if he does, he'd kill her.
After Fred tells Bob Carter of the origins of the mutants, Fred is killed by Papa Jupiter. Papa Jupiter then flees into the night and is seen berating his children for failing to kill all the Carters. Papa Jupiter sets his sons to rape Brenda and kill her mother. This proves his downfall when he is tricked into entering the rigged trailer where Brenda and Bob have set a bomb, which seemingly kills him. However, Papa Jupiter leaps back out, angry, but is killed by Bob.