star wars - What Sith Lords were turned to the Light Side?

I have heard of a ton of Jedi who have turned to the Dark Side and became a Sith (Exar Kun, Darth Malak). I've even heard of a few Jedi who have turned to the Dark Side and then found their way back to the Light (Revan, Anakin, Qel-Droma). But I cannot seem to recall any Sith who turned to the Light Side. I think I might have read of one, but I cannot remember the name or story.

Are there any Sith who have turned to the Light? Hell, have there even been any Sith that have turned to the Light Side and then returned to the shadows of the Dark Side?

Answer

Note: all individuals listed here are from Legends.

Sajar, formerly Darth Sajar, was a member of the Dark Council of the Sith Empire during the Great Galactic War. After dueling with the Jedi Master Tol Braga, he renounced the dark side and his title as a Sith Lord to become Braga's Padawan and study the light side.

Kel'eth Ur recorded a holocron that was stored in the Dark Temple on Dromund Kaas (capital of the Sith Empire). Though a Sith Lord, Kel'eth Ur's holocron promoted principles which agreed with the Jedi and the light side. Kel'eth Ur was apparently killed by the Sith Emperor for his heresy. Kel'eth Ur was a member of the Light Sith, a group within the Sith Empire that supported the Empire but was aligned with the light side instead of the dark side.

Gravid was the Dark Lord of the Sith about five centuries before the events of the films. He did not totally renounce the dark side, but drifted to the light side during his reign as Dark Lord. He is notable in that he attempted to destroy Sith knowledge and treasures so that he could attempt to guide the Sith to what he viewed as a better path -- this attempt set back the Sith Grand Plan and forced later Sith like Darth Plagueis and Darth Sidious to attempt to re-discover lost Sith knowledge (such as transfer essence, which would allow a Sith to cheat death). His story is recounted from the Sith point of view in the novel Darth Plagueis:

A human Sith Lord whose short reign had elapsed some five centuries earlier, Gravid had been persuaded to believe that total commitment to the dark side would sentence the Sith Order to eventual defeat, and so had sought to introduce Jedi selflessness and compassion into his teachings and practice, forgetting that there can be no return to the light for an adept who has entered the dark wood; that the dark side will not surrender one to whom, by mutual agreement, it has staked a claim. Driven increasingly mad by his attempts to straddle the two realms, Gravid became convinced that the only way to safeguard the future of the Sith was to hide or destroy the lore that had been amassed through the generations—the texts, holocrons, and treatises—so that the Sith could fashion a new beginning for themselves that would guarantee success.