8 Villains Who Made Good On Their Second Chance
2. Jack - Mass Effect
Jack aka Subject Zero made her debut in Mass Effect 2, where she's introduced as an ultra-violent criminal and one of the most dangerous human biotics in existence.
Granted, Jack has one hell of a traumatic past, having been abducted by Cerberus as a child and tortured as a test subject, so she certainly has a better reason than most for her bloodthirstiness and general psychopathy.
Jack is one of the prospects for Mass Effect 2's climactic suicide mission, and though the precise outcome of Jack's story will vary depending on your own playthrough, if she survives the events of the game she reappears in Mass Effect 3 as a teacher to biotic students at the Jon Grissom Academy.
At this point Jack seems to be in a much happier, healthier place, ditching her prior single-minded, violent instincts and becoming a productive member of society, even attempting to protect her students during a Cerberus attack.
It's often said that hurt people hurt people, but by the end of the original trilogy Jack has well and truly broken that cycle.