Harvey Dent should have been a crusader, he certainly likes to make that claim he was. Maybe he started out in life as a good boy, but after graduating from law school and moving back to Gotham City Harvey Dent changed. He wasn’t especially mean, or cruel, but he wasn’t exactly honest. People liked to say its because he was a lawyer, but Harvey was dishonest even by cheap lawyer standards. He joined the Gotham City district attorney’s office and quickly rose through the ranks. He was never outright corrupt, but there were a lot of criminals that were charged and tried quickly on lesser sentences than they deserved. Harvey liked to think that he was keeping more criminals behind bars so that helped the city as a whole, and if he occasionally found himself with free dinners at restaurants that Carmine Falcone owned that was on Falcone.
Harvey was finally elected as Gotham’s district attorney shortly before the appearance of Batman. The Dark Knight’s appearance didn’t change Harvey, but it did change the way he dealt with the mob. He stopped subtly helping them, and they got angry. Harvey avoided several assassination attempts and it made him paranoid, and angry. He took more and more extreme measures to protect himself, he started blowing up at people for no reason and he started to make decisions on a whim often using a coin to make the decision. Harvey finally met his end as DA with a face full of acid during a trial. A small time thug that was testifying for HIM doused Harvey’s face. The acid didn’t kill Harvey but it finally broke him. When he woke up in the hospital two weeks later Harvey was a broken man. He’d been forced out of the DA’s office, his friends had abandoned him, the only person that would visit him was his friend from law school, Bruce Wayne.
Wayne promised that he’d use his wealth and power to help Harvey recuperate, but the ordeal had left Harvey with nothing but suspicion and anger. He fled the hospital, found the thug that had thrown the acid and made the punk choose. Heads or tails, live or die. The thug chose wrong.
Harvey fled further into Gotham’s underworld and there he found those willing to protect him for money, or even out of a sense of loyalty. He founded his own crude gang and joined the the ranks of the criminal underworld with a loan from Oswald Cobblepot. Harvey despises Cobblepot but he sees the necessity of dealing with the man. At least until he can deal with the man.
Harvey often clings to the pretenses of court procedure and legal tenets when handling situations, but the final arbiter is always the coin. A 50-50 chance.