Kel'eth Ur was a Human male and former Sith Lord of the reconstituted Sith Empire who resided on Dromund Kaas. By the end of his life, he taught that passion only led to temporary strength and that true strength was found in peace - a philosophy conventionally associated with the Jedi. In 4606 BBY, he was killed by the Emperor for his heresy, according to Alaric.
He recorded his knowledge in a holocron, which was found in the Dark Temple during the Cold War.