Moon-Boy was born into a tribe of ape-like beings known as the “Small-Folk” who made their home in the ”Valley of Flame”, a region of numerous active volcanoes. Moon-Boy’s connection with Devil Dinosaur began on the day he came across a female dinosaur being attacked by a rival tribe known as the “Killer-Folk”. The female was killed, as well as two of her three young. The third did not die however, but was transformed when the Killer-Folk attempted to burn him to death with their torches. The fire permanently scorched the young dinosaur's skin bright red. Moon-Boy cared for the orphaned creature after its ordeal and named him "Devil".
Ostracized from his tribe because of his association with Devil, Moon-Boy and his red companion became wanderers. Devil and Moon-Boy’s wanderings eventually took them to distant times and worlds. After several trips to the modern era of Earth-616 via magic, time travel, and teleportation by mutants, the pair eventually settled in the Savage Land of Earth-616.
Later, Moon-Boy became separated from Devil when he was removed from the Savage Land and taken to New York City by the Heroes for Hire mercenary team who were hired by S.H.I.E.L.D. scientists to retrieve the “Homo habilis” so that they might study his DNA.
The squad was eventually able to stop Stegron, but after learning that Stegron was merely attempting to rescue Moon Boy, Reptil insisted on reuniting him with Devil Dinosaur. With help from Tigra, Reptil was able to stage Moon Boy's death and escape. Tigra contacted Ka-Zar, and he and Reptil accompanied Moon Boy back to the Savage Land.