Revan was a Sith Lord and the namesake of the Sith Eternal army’s 3rd Legion. Since the history of the Sith was kept hidden from the galaxy, only Sith cultists knew the significance of Revan’s name.
Sith trooper legions were each numerically identified and additionally named after an ancient Sith Lord. The Revan Legion was activated in 35 ABY along with the rest of the Sith Eternal’s forces during the war between the First Order and the Resistance.
An ancient Sith Lord named Revan was reestablished in the current Star Wars canon with a mention in Star Wars: The Rise of Skywalker: The Visual Dictionary, a 2019 reference book written by Lucasfilm Story Group member Pablo Hidalgo. The visual dictionary accompanied the film Star Wars: Episode IX The Rise of Skywalker, which were both released on December 20th.
Revan was originally introduced in the Star Wars Legends continuity in BioWare and LucasArts‘s 2003 video game Star Wars: Knights of the Old Republic. In Legends, Revan was a Jedi Knight who broke away from the Jedi Order, became a Dark Lord of the Sith, and formed a Sith Empire that waged war against the Order and the Galactic Republic. While experiencing amnesia, the former Sith was retrained as a Jedi to confront the Sith Empire, Revan’s own creation. As the playable character of the game, Revan’s physical characteristics and gender were customizable by the player for gameplay purposes; the 2005 reference book The New Essential Chronology then established Revan’s gender as male and canonized the light-side ending. Following the events of the game, Revan eventually confronted the True Sith and helped destroy its leader.