The double-headed coin is the instrument used by Two-Face to determine the course of his actions between good or evil. The coin's history and background has changed over the time and there have been many coins as oppossed to a single, exclusive item.
The double-headed coin belonged to the criminal "Boss" Moroni and it was found in a crime scene with his fingerprints on it. Harvey Kent used the coin as evidence in the trial against Moroni. Unfortunately, Kent's face was scarred in half by acid thrown at him by Moroni. Losing his sanity, Kent became the criminal Two-Face and decided to leave his decisions upon fate. For this, he scarred one side of the double-headed coin to use it as the instrument that would help him decide between good and evil.
After Kent's face was surgically restored, he allowed Batman to keep the coin among his many other collected items in his secret hall of trophies.
A second coin was created by former actor turned criminal called Paul Sloane, who was accidentally scarred just like Two-Face. The accident broke his mind and he used a prop coin to turn it into a double-headed coin. When Batman captured Sloane, he also remove the coin from his possession.
The original coin was eventually stolen by the third Two-Face impersonator, George Blake, who also used a couple of custom made coins on his crimes. However, Blake didn't follow the coin's rules and he just followed its decision according his own convenience. After Batman captured Blake, the coin returned to Batman along with the fake ones.
It was later revealed that Dent had a duplicate of the double-headed coin, which he used to start a second wave of crimes as Two-Face. After this revelation, it is impossible to know for sure how many other similar coins were created and used by the criminal.
Christopher Dent used to keep several double-headed coins as personal items he used to physically abuse of his son, Harvey. Making the small child believe that he had a chance to avoid punishment if the coin landed on tails, Christopher abused the "game" in order to beat Harvey senselessly.
Years later, a deranged Christopher gave the adult Harvey one of the coins, and he kept it with him as a lucky charm to prevent his evil side from taking over. However, during the fateful moment in which his face was scarred, the coin was also marred on one side and the manner in which the events unfolded caused Harvey to become Two-Face and use the coin as the instrument to take action.
- In the movie Batman Forever and the episode Two-Face, Part II of Batman The Animated Series, Batman easily defeated Two-Face by throwing up multiple quarters and silver dollars while the villain was in the middle of flipping his coin. The former resulted in death of that universe's Two-Face.
- In the movie The Dark Knight, Dent was burned in a fire instead of hit with acid or scarred by Maroni. Following his updated origins, one side of the coin was scorched instead of scarred.