Unidentified warrior (Carnelion IV)

This unidentified sith is first shown in battle in a hologram that Sera show Obi-Wan Kenobi on arnelion IV. The sith was first believed by Sera to be a Jedi, but was corrected by Obi-Wan when he heard that the sith had a red lightsaber.

Behind the scenes
The identity of the sith is still not confirmed, but the appearance is similar to that of Darth Revan who currently only exists in Legends. Revan was first introduced in the video game Star Wars: Knights of the Old Republic, which was released by BioWare and LucasArts in 2003. As the player's character, Revan's gender and physical appearance are customizable by the player, which makes it hard to assume this sith's race and gender, but Revan was previously established as a human male in the Legends continuity.

In 2011, Revan was slated to appear in Ghosts of Mortis, an episode of the third season of the Star Wars: The Clone Wars television series. Revan would have appeared as a Sith Lord alongside Darth Bane as advisors to the Son, but they were cut from the episode in late production. The show's director, Dave Filoni, was apprehensive of using the scene, and the scene was removed at George Lucas's request because it conflicted with Lucas's view on the Force. The scene made it to the animatics stage and could be viewed in the bonus content on the Blu-ray edition of Star Wars: The Clone Wars The Complete Season Three. The scene is set in the Well of the Dark Side on the planet Mortis, where the powerful Force wielder known as the Son confronts dark side spirits about the recent death of his sister, the Daughter, at his hands. The spirit voices tell the Son to embrace his pain and resentment, and when he questions their identities, giant apparitions of Darth Bane and Darth Revan appear to the Son, proclaiming their intent to ensure the dark side's supremacy. Speaking of another's existence who will control the galaxy, Revan and Bane warn the Son that control over Anakin Skywalker, the Chosen One, is the key to the Son's success.

Appearances

 * Obi-Wan & Anakin, Part IV
 * Obi-Wan & Anakin, Part V