Gavar Khai, who accidentally killed the Sith
A Sith who lived around the time of the Second Galactic Civil War was a member of the Lost Tribe of Sith, a group from the planet Kesh. In 44 ABY, the Sith member was chosen to accompany High Lord Sarasu Taalon's convoy of eleven ChaseMaster frigates to ally with Jedi Grand Master Luke Skywalker for a mission to find the female dark side being Abeloth. However, afterward, Taalon planned to betray and kill Skywalker and force Abeloth to serve the Sith Tribe.
After arriving on Abeloth's planet and finding the being, the allied forces engaged her in combat. The Sith, along with Taalon, Skywalker, Sith Saber Gavar Khai, and one other Sith, battled with Abeloth. However, she suddenly disappeared, and Khai's lightsaber strike, intended to hit Abeloth, passed through the empty space where she had been a moment before and carved through the Sith, resulting in the Sith's death. As Abeloth reappeared and the battle continued, carnivorous vines began to rip apart the dead Sith's corpse.
The Sith was Force-sensitive, and Taalon considered him very powerful, as the the High Lord had only chosen the strongest Sith to accompany him on the mission to Abeloth's planet.
The Sith member appeared in Allies, the fifth novel of the Fate of the Jedi series, which was written by Christie Golden and published in 2010.