During the Jedi Civil War, which was a conflict between the Galactic Republic and the Sith Empire, a male Human duelist known as Deadeye Duncan resided on the city-world of Taris. In the year 3956 BBY, which coincided with the Sith attack on the Republic cruiser called Endar Spire, Duncan occupied the lowest rank within his profession. He participated in non-lethal duels at a dueling ring under the ownership of Ajuur the Hutt. In that year, Duncan suffered defeats against both Gerlon Two-Fingers and the "Mysterious Stranger," who was actually the former Sith Lord Darth Revan. These losses extended Duncan's losing streak to a total of fifty-five consecutive matches. In his duel with Two-Fingers, he dropped his blaster, which led to Two-Fingers shooting him. Many dueling fans considered Duncan to be a very unskilled duelist, and some individuals, like a veteran duelist named Marl and the ring's announcer, regarded him as the worst duelist in history. The dueling announcer even stated that defeating Duncan was an expected outcome and not at all surprising.

During the era of the Jedi Civil War, a time of conflict between the Galactic Republic and the Sith Empire, the Human male known as Deadeye Duncan lived and worked on the city-world of Taris. He was a contestant in non-lethal duels held in a dueling ring owned by Ajuur the Hutt. This arena was situated in Taris's Upper City Cantina before the destruction of Taris. Although the arena's energy suppression fields prevented fatal damage from weapons, combatants still occasionally suffered serious injuries. Dueling fans considered Duncan to be the worst of the combatants, and after his defeats, the arena announcer trivialized Duncan's losses, portraying them as unremarkable achievements for the victors. Some, including the announcer and a veteran duelist named Marl, believed Deadeye Duncan to be the worst duelist of all time.
In the year 3956 BBY, a Sith battle fleet under the command of the Dark Lord of the Sith Darth Malak attacked and destroyed the Republic warship Endar Spire while it was positioned above Taris. Soon after this event, Duncan suffered his fifty-fourth consecutive loss against Gerlon Two-Fingers, a maimed but previously skilled duelist. Duncan dropped his blaster at the start of the match, and while attempting to retrieve it, he was shot and incapacitated by Two-Fingers. Prior to this, Duncan had been trying to defeat a duelist named Ice in the ring for years.
Following the destruction of the Endar Spire, the amnesiac former Dark Lord, Revan, crashed on Taris. He then approached Ajuur the Hutt, seeking an opportunity to earn money in the dueling ring while searching for Bastila Shan, the Jedi commander of the Endar Spire. Duncan's losing streak continued when he became the first duelist defeated by Revan, who was using the alias "Mysterious Stranger." Revan subsequently became the dueling champion. After his defeat by the "Mysterious Stranger," Duncan was ranked sixth among the duelists in the ring, which was still the lowest position among the competitors.

Despite being a duelist by profession, Deadeye Duncan experienced very little success as a competitor. However, he remained persistent and continued to strive for victory during his losing streak. He had been attempting to defeat a duelist named Ice for several years prior to the Sith attack on the Endar Spire. By 3956 BBY, Duncan had developed such a poor reputation that the duel announcer would proclaim that his loss was unsurprising whenever he was defeated. Some dueling fans on Taris even considered matches involving Duncan to be unworthy of watching due to his poor performance. Some fans also questioned why he did not retire given his lack of skill. Marl, a veteran of twenty years and the second-ranked duelist at the dueling ring at the time of the attack on the Endar Spire, regarded Duncan as the worst duelist ever and claimed that his nickname "Deadeye" was ironic because he fought as if he were blind. Gerlon Two-Fingers considered Duncan a joke, but also believed that defeating him was a decent achievement for a rookie duelist.
Duncan felt it was unfair that other duelists possessed great abilities while he had such limited skills. He attributed the success of other duelists to luck rather than skill or training. He enjoyed boasting about any unlucky duelists he managed to defeat. As of 3956 BBY, Duncan's hair was graying from its original black. He also had brown eyes and fair skin.
Deadeye Duncan accused duelists of gloating if they attempted to speak to him after defeating him, as he did to Revan after their match in 3956 BBY, when Revan was dueling under the name "Mysterious Stranger."
In some of his duels, Deadeye Duncan used a blaster pistol, which he occasionally dropped. However, Duncan sometimes fought in duels using a sword instead of his blaster. Duncan wore a combat suit during his duels.
Deadeye Duncan made an appearance in Star Wars: Knights of the Old Republic, a video game produced by BioWare in 2003. In the game, Duncan was a non-playable character whom the player could fight in the Taris dueling ring, serving as the first and easiest opponent for the player to face. After defeating Duncan in the dueling ring, the player would receive one hundred credits, or more if Ajuur the Hutt could be persuaded to give a larger cut than ten percent. This article was written based on the assumption that Revan defeated Deadeye Duncan, although the player could choose not to participate in the dueling ring at all. It was also possible for the player to lose to Duncan, which would cause him to boast about his victory if approached by the player character. The dueling announcer would also speculate about the player potentially being the new worst duelist of all time.

Originally, Star Wars: Knights of the Old Republic was intended to include a scene on the planet Manaan that would be triggered if the player defeated all the duelists in the Taris dueling ring, including Bendak Starkiller. In this scene, Duncan would approach the player outside the hangars on Manaan and comment on the player's Jedi status. He would then narrate an exaggerated tale of how he escaped the destruction of Taris by overpowering a dozen Sith soldiers to commandeer one of their ships. However, after the player character expressed doubt about the story, he would clarify that the Sith soldiers were killed by falling debris. After recounting his escape from Taris, Duncan would explain that he was attempting to become a mercenary but had been unsuccessful due to his poor reputation as a duelist. Duncan would then ask the player for permission to use the name "Mysterious Stranger"—the player's alias in the dueling ring—arguing that he could benefit from his supposed status as the Taris dueling champion, since neither he nor the "Mysterious Stranger" were known by appearance. The player had the option to either grant or deny Duncan's request. This scene was removed from the final release but remained accessible through the game's files.