When Harvey Dent was interrogating Boss Maroni during a court hearing, Maroni tried to kill Harvey by throwing acid into his face. Although Batman tried to save Harvey, the acid managed to burn the left half of Harvey's face. The acid burned far enough through his head that part of his brain was damaged, and made Dent half psychotic and homicidal. Dent also blamed Batman for the condition that he was in, and wanted to get his revenge on the Dark Knight.
Dent was eventually arrested and retained in Arkham Asylum. Two-Face escaped from his cell on the second anniversary of his arrest; his escape being discovered by Dr. Burton, who contacted the Gotham City Police Department.
Two-Face and his thugs robbed the Second Bank of Gotham. They had taken hostages and looked like they were going to get away when Batman intervened and stopped the robbery. However, Two-Face escaped.
Later on, Two-Face traveled to the circus looking for Batman. With the circus currently holding a fundraiser that was attended by Gotham's elite, Two-Face concluded that the odds were excellent that at least one of them knew the Dark Knight's identity if they weren't Batman himself, and threatened to blow the place up unless his enemy turned himself over (although the subsequent riot in the circus prevented Bruce Wayne from obeying his order). He was responsible for the origin of Robin because when The Flying Graysons tried to stop him, they were all killed by Two-Face. Dick, the youngest Grayson, survived and went on to join Batman as Robin.
At his lair, which was split in half like his personality, Two-Face had two henchwomen, Sugar and Spice, who worked for him. Spice favored his 'dark', scarred side, while Sugar favored his 'good' unscarred side. While the three were about to have Harvey's favorites, the Riddler showed up and offered Two-Face a proposal: Two-Face helped the Riddler steal enough money so he could become Gotham's cleverest carbon-based life form, and in return, the Riddler would help him discover the identity of Batman so that they can use it to plot Batman's downfall. With a flip of a coin marking heads in favor of the deal, Two-Face agreed to the Riddler's terms.
Two-Face joined forces with the Riddler and they committed crimes together. The two robbed a building and soon discovered Batman's true identity: Bruce Wayne.
After they discovered Batman's true identity, Two-Face, Riddler, and the former's henchmen infiltrated Wayne Manor on Halloween Night. While Two-Face and his henchmen attacked Bruce and Dr. Chase Meridian while he flipped his coin, which kept landing on good side up, and prevented him from doing anything bad, Riddler destroyed the Batcave. As soon as the scarred side of his coin came up, Two-Face shot Bruce with his pistol, and grazed him in the head. Two-Face wished to finish him off, but Riddler intervened, kidnapped Dr. Meridian, and left behind another riddle.
At the Riddler's Lair, Claw Island, Batman and Robin got separated. Robin eventually fought Two-Face and even had the chance to kill him, but didn't, because he refused to be like him. Two-Face then managed to capture Robin, and brought him to Riddler. Batman confronted the two villains and they revealed that they had both Robin and Dr. Meridian captured, and then Riddler sent them falling to their deaths, which left Batman to save them. Batman managed to save the pair, but Two-Face flipped his coin and decided that he'll go after them. While Two-Face waited to see what side his coin landed while he had his gun pointed at the trio, Batman tossed up a bunch of identical coins which made Two-Face panic and he slips and falls into the watery bed of spikes, which ended his life once and for all and the deaths of Dick Grayson's family were finally avenged.