Chronos
He only wanted to watch the world burn – was that so much to ask? If you asked the Legends, they would answer "yes", which greatly annoyed him. He hated every moment he spent on that spaceship, as well as those stupid meetings – Vandal this, Savage that. Why did they even still ask him to come to these meetings? Just point him to a target and he could finally burn some stuff.
Then the time pirates came along, Mick made a wrong gamble and Snart had to take care of him. He could not kill his partner and left the unconscious Mick in a time period he did not know. Needless to say, when Mick woke up, he was pissed at his former partner. The feeling stuck with him, even after the Time Masters came to pick him up.
He was grateful for their help. Not that he was ever going to admit it or say it out loud. They saved him, clothed him and gave him everything he wished for. He traded away his heat gun for something more 'sophisticated' – it caused more damage and items around the impact center exploded. He loved his new weapon.
They did not have to warp his mind to join the Time Masters. He went out on his own accord, though he rejected that horrid nickname "Chronos". Still, that was how the Legends knew him, and he wore a helmet to protect the younger Mick from seeing Chronos and breaking time.
Chronos remained a thorn in their side for a long time and eventually, he had Snart at gunpoint. He refused to show Snart the same mercy he had once shown his friend. One Legend less to worry about. His former team subsequently put him higher on their priority list.
With each passing day, the Time Masters' grip on him faded away and despite their attempts to keep Chronos close, he slipped further away. And one day, out of the blue, he snapped. He is and always will be an arsonist, and explosions wouldn't do the trick anymore. So he set fire to the Vanishing Point. Those who tried to escape were blown to bits, and Mick enjoyed every moment of it. He stared at the flames for hours on end, having all the time in the world to enjoy the fall of the Time Masters. Of course, Rip Hunter caught wind of the situation and came with the Legends, but Chronos had already left by then.
Then, he traveled back to the time they met Aldus Boardman. Mick and the others were there to protect him from Chronos, which did not work out for them the first time around. But Mick – a third Mick, after he set the Vanishing Point aflame – stepped in and took the hit, so Aldus lives. The wounded Mick had been brought aboard, where he and the youngest version of Mick stood eye to eye.
Having successfully interfered in a time period he had already interfered in, Mick had created a paradox. Rip Hunter, knowing the consequences, refused to initiate a time jump, but the oldest Mick forced Gideon to do the time jump.
The Waverider crashed in downtown Los Angeles, where the big Ben proudly chimed and dinosaurs walked the streets. With a sufficient distraction and every last bit of strength he has, older Mick manages to either kill or seriously maim every single one of them – it was a pleasure to watch Leonard die for the second time. Those who didn't die had fled, and soon the older Mick faded from existence.
Younger Mick was left alive, and he wandered out of the Waverider. He took a moment to observe his surroundings before a crazy grin appeared on his face and he set out to do what he did best. Through the chaos of a time paradox, Mick finally watched the world burn.