Talk about it here.
Holliday moved to the town of Tombstone with his girlfriend, Kate Fisher. There he befriended the local marshal, Wyatt Earp, and started a business as a dentist. He was setting up this business when Kate came to warn him that the Clanton brothers (Ike, Billy and Phineas) had come to kill him after he killed their brother, Reuben Clanton.
The First Doctor visited Holliday's dentistry to have his tooth removed. As he was the first ever customer, Holliday performed it for free. While he was with Kate in a back room, Seth Harper, an associate of the Clantons, entered and took the Doctor to be Holliday. He left after telling the Doctor to meet him at the Last Chance Saloon.
Seeing this as a chance to fool the brothers, Kate and Doc dressed the Doctor in regalia akin to that of Doc, even giving him a gun with Holliday's name engraved upon it. After finding a message from Kate saying she had gone to the saloon, Doc went there and entered through a back entrance. He watched as the Clantons threatened the Doctor, believing him to be Doc. Holliday fired at the roof, causing chaos below. Dodo Chaplet was alerted by the shot and met Holliday on the stairs. He threatened her and forced her to return back to her room. Doc also went to Dodo's room and Kate joined them. To pass the time, Doc and Kate played cards.
After seeing a mob pass by looking to lynch the Doctor, and also carrying his operating chair, Doc decided to go out. On the way down, Kate called after him, causing Seth Harper to identify him as the real Doc Holliday. However, Doc was faster on the draw and killed Seth.
Doc, Kate and Dodo then left town and went to another saloon not far from Tombstone. While fetching food for his companions, Doc met a man whom he had wronged in the past and killed him in the ensuing fight. Impatient to return to her friends, Dodo threatened Doc with a gun, telling him to take her back to Tombstone. Although he was armed and Dodo posed little threat, he agreed and told Kate to stay in the saloon. Returning to Tombstone, Doc sided with Wyatt and Virgil Earp to fight the Clantons. This was largely because Johnny Ringo had sided with them and kidnapped Kate.
The two sides met at the O.K. Corral and a gunfight ensued. Ringo managed to get behind Doc but Dodo warned him of the danger. Ringo took Dodo as a human shield, forcing Doc to drop his gun. As Ringo moved to run, Doc pulled a second gun and shot him. He sat next to him as he died, telling him he had expected more from him.
Holliday regrouped with Wyatt and killed Billy Clanton. Together with Virgil, they killed Ike, the last of the Clanton brothers. Following this, Doc decided to leave town with Kate, largely because the sheriff, Bat Masterson, had issued a "Wanted" notice for Doc. Holliday gave this poster to the First Doctor who dropped it before leaving in the TARDIS, (TV: The Gunfighters) although it later appeared in a version of his TARDIS from another universe. (PROSE: Sanctuary)
In his last years, an ailing Holliday lived in a sanatorium in Colorado. He spent his days drinking heavily and waiting with a gun for any old enemies who wanted to kill him early. Shortly before his death on 10 November 1887, Holliday gave Ned Buntline a detailed account of an aspect of the gunfight which was not generally recorded in the history books, involving another Doctor. He seemed to die right after completing the story, only to revive, down a bottle of alcohol in three gulps rather than leave it, and then die. (PROSE: The Gunfighters)
Behind the scenes
In reality, Doc Holliday died on 8 November 1887.