Marvel Comics recently released their Star Wars Annual #4, which confirms a brand new Sith Lord that can be added to the Star Wars canon, named Darth Atrius. While there is still much we don't know about Darth Atrius, and we don't actually see this character in the comic, this story features Luke Skywalker and Darth Vader who had a brief connection to this ancient character. His inclusion in this comic also makes him one of the rare Sith Lords to be added to the canon, since Disney dismissed the Expanded Universe as Canon and re-labeled it the "Legends" universe.
Star Wars Annual #4 follows a smuggler named Sana Starros, who has tracked down the ancient weapons of Darth Atrius, a pair of crossguard lightsabers, similar to the controversial design used by Kylo Ren that was introduced in Star Wars: The Force Awakens. It was later confirmed on Star Wars: The Clone Wars that this design was once favorable to both Sith and Jedi alike, many, many years ago. This comic also makes it clear that the anger possessed by Atrius when wielding both these crossguard lightsabers at the same time, carried over to the weapons themselves, and can transfer over to their new owners.
Starros tries to sell the lightsabers to both Skywalker and Vader, but Vader insists that he needs both of the lightsabers for his purposes. Unfortunately for Vader, Luke senses the evil contained within the lightsaber and destroys it, while Vader does the same with his lightsaber, meaning all secrets these lightsabers may have contained about the mysterious Darth Atrius have all but disappeared. With all of that being said, Darth Atrius' inclusion in this comic could lead to more stories about his past, although Atrius' exact placing within the Star Wars timeline remains uncertain.
In the comic, when Luke gets a look at the Atrius lightsaber, he says it's older than any lightsaber he's ever seen before, which offers a hint at how long ago Atrius' reign as Sith Lord happened. While the Legends canon revealed a slew of Sith Lords in the past, there are only a handful that remain in the Star Wars canon, which means Atrius' reveal could be quite significant in stories that are yet to come, either on film, television, comics, or all of the above. Rian Johnson is currently developing a new Star Wars trilogy that revolves around brand new characters, and while it's unlikely that this new Sith Lord is one of those characters, anything is possible when it comes to Star Wars.
Darth Atrius joins the other known Sith Lords in the Star Wars canon, Darth Bane, Darth Plagueius, Darth Sidious, Darth Maul, Darth Tyranus and Darth Vader. The 33-page Star Wars Annual #4 was written by Cullen Bunn, with inkers Ario Anindito, Marc Laming, Roland Boschi and colorists Andres Mossa and Jordan Boyd. You can pick up Star Wars Annual #4 either in digital or print form on Marvel.com.