Jameson was born a giant to Rose Cotton and Sam Gamgee shortly after the two eloped in 1917. Although his grandfather, the Hulk, had been a giant, it was uncommon for the giant gene to appear more than once every 100 generations, and his parents had a test done to see what had gone wrong.
They soon discovered he was born deformed due to incest, and the two discovered they were mother and son, but stayed together to raise their son.
It is unknown if his parents loved him, but they raised him to be as normal as possible, going so far so as to change his name from Gamgee to the more normal name Jameson, and he grew up wearing business suits and sitting at a 20-story desk.
Growing jealous of James, Slash kicked him square in the chest sending him to a coma from which he can never fully recover, all of his immortal life.