Green Lantern's arch-nemesis is Sinestro, a former Green Lantern and leader of the Sinestro Corps, a group of villains who use a yellow power ring fueled by fear. Sinestro is often depicted as a complex and conflicted character, with a tragic backstory and a desire to impose order and control on the universe. His battles with Green Lantern are some of the most iconic and memorable in comic book history.