In the 2008 film the Dark Knight, Harvey Dent was Gotham's stellar District Attorney who was nicknamed "The White Knight" for his lawfulness and morality in fighting the organized crime of Gotham. All of this changed however when The Joker kidnapped both Harvey and his fiancee Rachel Dawes and left them tied up in separate buildings with explosives as whichever person Batman didn't go to save would be blown up.
Batman saved Harvey resulting in Rachel's death although Harvey was scarred in the incident as half of his face got covered in gasoline which burned off much of his flesh. Following an encounter with the Joker, Harvey went insane and obsessed with duality and chance leading him to hunt down everyone he saw as responsible for Rachel's death and give them a 50/50 chance of punishment. Ultimately this resulted in Batman killing him by pushing him off a ledge when he threatened to kill Commissioner Gordon's son as vengeance.