...A-Bomb's origin hasn't been revealed, at least not to my knowledge. He showed up in the Hulk's book and quickly became cannon fodder to the Red Hulk (although he performed much better than his predecessor... and anyone else for that matter up until Hulk #6). What was shown is his (A-Bomb's) durability is perhaps off the charts, as evidenced by him withstanding punches which registered a magnitude of 10 on the Richter Scale (although how the surrounding area wasn't decimated by a force equivalent to a one million megaton detonation I'll never know.... apparently somebody didn't do their homework).
> How this happen???