User blog comment:Dragonsblood23/Robbie Rotten's Super Villainous Toruney: The Quest to be Robbie's Number 2 Villain/@comment-25263388-20170213002321/@comment-3401602-20170213005430

Every playable character in Overwatch is called a "hero" but most are far from it.

According to the Overwatch Wiki on Junkrat's story:

The attack on the Australian omnium's fusion core forever altered the landscape of the Outback. After the detonation, the area was transformed into a harsh, irradiated wasteland, littered with debris and the twisted fragments of the ruined facility, and unlivable to most.

Junkrat was one of them, eking out a living reclaiming metal and components from the ruins. Like many others, he was affected by the lingering radiation. This touch of madness made him ideal for handling dangerous explosives, a love which he turned into an obsession.

He came to notoriety when he discovered an extremely valuable secret in the bones of the omnium. Though few knew the nature of what he found, he was nonetheless pursued by bounty hunters, gangs, and opportunists wherever he went, until he made a deal with the Junker enforcer Roadhog, who grudgingly agreed to be his personal bodyguard in exchange for a fifty-fifty share of the spoils.[1]