15 Video Game Heroes Who Became Villains 

Sarah Kerrigan – Starcraft/Starcraft 2

While Kerrigan never had the best home life, what with psychic conditioning and military training as a young girl, her adult life that we see within the first chapter of Starcraft in the Sons of Korhal shows her as an idealist at the very least. A fateful betrayal by a trusted leader would give rise to the Queen of Blades, when she was abandoned to a Zerg Swarm and altered on a DNA level into a violent psychic force for violence on a magnitude greater than the sector had ever seen. The feats of deception and violence Kerrigan would unleash would see her build the Zerg swarm upon untold mountains of dead bodies.