Gotham City District Attorney Harvey Dent was nicknamed "Apollo" by the media, because he was charming, good-looking and seemingly untouchable. He was dedicated to his job of upholding law and order, and became one of the first supporters, allies and even friends of the Batman. At the time of his job as D.A., the worst criminal threat in Gotham was nigh omnipotent mafia boss Carmine Falcone, "The Roman." He forged a triumvirate with Batman and Commissioner James Gordon to bring the man down within the law, no matter what the cost. His slightly angrier temperament led Batman and Gordon to distrust him slightly, believing there was a possibility he might be the mysterious "Holiday" killer who was gunning down mob members at the time. The alliance ended tragically when Sal Maroni, believing Dent to be responsible for the death of his father, threw acid in his face during a trial. Harvey was horribly scarred on the left side of his face and his left hand.
Harvey escaped from the hospital and descended into madness. He became obsessed with duality and opposites, and developed a second persona, the villainous Two-Face, to compliment the law & order obsessed Harvey Dent. As Two-Face, his trademark was crimes involving the number two. His obsession even shows in his clothes, which are usually composed of two halves made out of very different materials. He carries a double-sided coin with one side scarred at all times.
In the aftermath of the earthquake that left Gotham City in shambles during the events of "Cataclysm," Two-Face kidnapped Commissioner Gordon and put him on trial for his actions during No Man's Land, with Two-Face as both judge and prosecutor. Gordon played upon Two-Face's split psyche to demand Harvey Dent as his defense attorney. Harvey Dent cross-examined Two-Face and won an acquittal of Gordon.
It was also during this time that Two-Face met GCPD detective Renée Montoya. Montoya was able to reach the Harvey persona in Two-Face, and was kind to him. He fell in love with her, though the romance was one-sided. After the earthquake that ravaged Gotham, Two-Face outed her as a lesbian and framed her for murder, hoping that if he took everything from her she would be left with no choice but to be with him. Montoya was furious, and the two fought for control of his gun until Batman intervened, putting Two-Face back in Arkham Asylum.
A short time later, Two-Face met the brilliant surgeon, Dr. Thomas Elliot. Although Elliot specialized in neurosurgery, he was competent enough to repair Harvey's face via plastic surgery.  Harvey Dent's sanity was restored, and the menacing "Two-Face" persona seemed to be gone forever. Thomas Elliot was also the villain known as Hush, and he had hoped to manipulate Harvey into acting as one of his many pawns in a campaign against Batman. With renewed sanity, Harvey stood by the side of law and order and betrayed Hush, catching him in enough time to save Batman's life, and shooting him into the Gotham river.
Having regained his trust, Dent was trained and conditioned by Batman to act as Gotham's primary vigilante protector when he, Robin and Nightwing all took a one-year hiatus to train during the Lost Year. When Batman returned, a series of murders occurred implicating Harvey and involving Two-Face's M.O.. When confronted on the issues by Batman, in his anger at being distrusted, the Two-Face persona resurfaced, and talked Dent into scarring his face and returning to his life of crime.
Harvey Dent has returned to the Two-Face identity and committing crimes.
Two-Face is not consistently evil; every time he contemplates a crime, he flips his two-headed coin. Only if the coin came up scratched-side did Two-Face go ahead and commit the crime, never questioning the result of the toss. This compulsion is a compromise between Dent's evil "Two-Face" personality and his former, law-abiding self. Over the years, he has been shown to rely on the coin to different degrees. Sometimes to decide whether or not to commit a crime, sometimes to decide whether or not to do something good, like save someone. He will even go out of his way to do good deeds if the coin mandates. In the questionable "Arkham Asylum: A Serious House on Serious Earth" one-shot, the doctors at Arkham were shown to have weened him off of the coin, and onto a die, then a pack of tarot cards. With the die, instead of only good and evil, he is given six different options, and with the tarot, seventy-eight. Two-Face is shown to be completely dependent, and is unable to even decide to go to the bathroom before sorting through the cards, wetting himself. During Countdown, when he is being deported to the "Hell Planet" along with the other villains in Salvation Run, Pied Piper and the Trickster offer to break him out of Belle Reve after defeating his escorting guards. Two-Face flips the coin, and it comes up un-scarred, so he declines, and instead simply waits patiently in the middle of the hallway for more guards to show up.
Over the years, various attempts have been made to repair his facial scars, but none have successfully cured his insanity long term; although he has briefly returned to his Dent persona, he has ended up simply destroying one side of his face and becoming Two-Face once again.
Powers & Abilities
Harvey uses a two-headed silver dollar, one side of which is defaced, the other side clean. Flipping the coin dictates Harvey when making any significant life decisions. If the coin lands on the scarred side, Two-Face will pursue acts of evil. If the coin lands on the unmarked side, he is compelled to commit acts of good. At one point Dent as Two-Face was so dependent on the coin for any of his criminal acts that he could be easily defeated by taking the coin away from him or preventing him from seeing the result of the flip. The original Earth-Two Two-Face was usually shown at this level of dependency Kent. Dent has since lessened his dependency on the coin flip to whether an situation should be implemented, rather than each individual act.
Typically Two-Face uses a variety of automatic and semi-automatic handguns to conduct his criminal affairs. He usually carries two.