Two-Face first appeared in Detective Comics #66 in 1942 as Harvey Kent, a Gotham City district attorney leading a case against a gangster named "Boss" Moroni. When Kent reveals evidence condemning Moroni, the gangster throws acid in Kent's face, permanently disfiguring him. His wife Gilda's adverse reaction to his face causes Kent to snap and turn to a life of crime. However, a year later in Detective Comics #80, Kent's life of crime meets a happy conclusion when his assistance of Batman earns Kent a truncated prison sentence and reconstructive surgery for his face.
Finally, in 1954's Batman #81, the reformed Harvey Dent attempts to foil a robbery and falls victim to an explosion that undoes the plastic surgery that helped him lead a normal life, forcing him to return to the role of Two-Face.
In 1946, the parallel Batman newspaper strip introduced Two-Face under a different alias. This time, he was Harvey Apollo, a handsome actor who was scarred with acid as revenge for his testimony in the trial of a criminal named Lucky Sheldon.
Other short-lived versions of Two-Face followed, with Batman #50 in 1948 introducing a new Two-Face that turned out to be the butler of Harvey Kent (now renamed Harvey Dent) in disguise. Batman #68 in 1951 reintroduced a new Two-Face. As in the newspaper strip, he was a handsome actor named Paul Sloane. Rather than suffering the attack of a mob boss, Sloane becomes Two-Face when a reenactment of the Two-Face's origin for TV results in real acid being thrown in his face due to the scheme of a jealous prop technician. In 1952's Detective Comics #187, a theater manager named George Blake poses as Two-Face to commit insurance fraud, framing the still-reformed Harvey Dent in the process.
In the years since his initial appearances, Two-Face's origin has been revised to include an abusive childhood that left him secretly schizophrenic and full of rage, which he quelled by working to maintain law and order as Gotham City's district attorney. As in his first appearance, an acid attack from a mob boss scars half of his face, causing Dent to snap and lead a life of crime as Two-Face.
Besides his half-disfigured face, Two-Face is known for his suits, which are asymmetrical in design and coordinated to his face. Typically the half corresponding to the undamaged side of his face will be a solid color while the half corresponding to his scarred side will have a more intricate design, usually plaid.
Two-Face's crimes tend to be based on the number two, a result of his obsession with dualism, a trait further cemented by his need to make decisions by the flip of a two-headed coin, one side of which is scratched. When the clean side turns up, Dent's good side will prevail in the decision making. However, when the scratched side turns up Dent will act evilly.
Two-Face appears as a villain in several Batman adaptations. Billy Dee Williams plays Harvey Dent in Tim Burton's 1989 "Batman" film, though the Dent does not become Two-Face until 1995's "Batman Forever," this time played by Tommy Lee Jones. Harvey Dent does not appear in Batman films again until Aaron Eckhart's portrayal of both Dent and Two-Face in "The Dark Knight" in 2008.
In animation, Harvey Dent first appears (voiced by Richard Moll) in the 1992 "Batman: The Animated Series" episode "On Leather Wings" and transforms into Two-Face in "Two-Face: Part 1." The 2008 animated series "Batman: The Brave and the Bold" has also introduced Two-Face under the vocal talents of James Remar.