Star Wars: Every Sith Who Turned To The Light Side

Darth Gravid was a Sith who worked alongside his apprentice, Darth Gean. Gravid began researching the Jedi simply to learn more about his enemy, but the more he read, the more he realised the Light Side's philosophies could be implemented into Sith lore to make it stronger. Over time, he found the Sith ways to be inconsistent and contradictory and so, destroyed countless files on the Dark Side, which encouraged Gean to slay him.

In the novel, Darth Plagueis, the titular Sith Lord told Darth Sidious that Gravid's actions set back his plans for galactic rule by centuries. Even though Gravid started off as a Sith, he has done more damage to the Dark Side than almost any Jedi.