The moniker "Mysterious Stranger" was bestowed upon Revan by Ajuur, the Hutt, during Revan's participation in the gladiatorial tournament held on Taris. This tournament took place within the confines of the Taris dueling ring, located inside a cantina in the Upper City. The reason for this name was Revan's recent arrival on the world, as he had just reached the city following his and Carth Onasi's escape from the attack that destroyed the Endar Spire.
Although Revan, operating under a newly created identity, preferred to fight using his assumed birth name, Ajuur believed that "Mysterious Stranger" had a better ring to it. Furthermore, Carth suggested this anonymity as a precaution, fearing that the Sith forces controlling Taris might have found a crew manifest from the Endar Spire before it was destroyed. As the Mysterious Stranger, Revan proceeded to battle and triumph over Deadeye Duncan, Gerlon Two-Fingers, Ice, Marl, and finally Twitch. Upon securing this victory, he was crowned the Taris Dueling Champion, earning him the right to a death match against Bendak Starkiller.
Centuries later, the title "Mysterious Stranger" resurfaced when Dominaire gave it to the Alliance Commander who was competing in the Eternal Championship.
Although originating from a canonical source, the dueling sequence is an optional side quest in Star Wars: Knights of the Old Republic. Players are not required to participate in these events. Moreover, the duel to the death with Starkiller represents a dark side choice, potentially rendering it non-canonical.
Players are free to name their character as they wish, but within the story, Ajuur always insists that the player fight under the name 'Mysterious Stranger' because it is more attention-grabbing. This is due to the announcer's voice (during the duels) being pre-recorded, preventing the use of custom names. In the German localization, Revan is referred to as "Mysterio" instead of "Mysterious Stranger".
A scene that was removed from the final game showed Revan possibly encountering Deadeye Duncan on Manaan. After discovering that his opponent was a Jedi, Duncan requests permission to use the "Mysterious Stranger" alias to boost his reputation, and the player could choose to grant or deny his request.