Megaton once went by the name Stewart before an event during his job.

Megaton was once a miner in the coal industry, his job was to lay TNT down on tough rock and then blow it up. one day, this job he'd done with ussual perfection went pear shaped. Megaton prematurely detonated the TNT and was subjected to a torrent of debris and a powerful shockwave. miraculously, Megaton survived with only a scar just under his eye. this event gave Megaton the idea that it was a sign, a sign that led him to become completely insane and obssesed with all things that go BOOM!

Megaton soon joined a terrorist group simply for the fun of blowing stuff up before the Rouxians arrived. upon their arrival, Megaton fought back only to be captured and nearly assimilated, his arm however did not survive this encounter. upon escaping the Rouxians, Megaton fled from Utopia in search of somewhere that didn't try to kill him...

That's when he met Cerene and Bleak.