4. Darth Vader (Star Wars)
Formerly a Jedi Knight, Anakin Skywalker - as he was previously known - was manipulated in to turning to the dark side by an evil Sith Lord; Darth Sidious. As Sidious transformed the Republic in to the Galactic Empire, Vader became his right-hand man and enforcer - developing a reputation as a man who took charge with an iron fist, killing any servants who didn't do their job properly. As a result, Vader also became widely feared around the entire galaxy, and this is what makes him a more than suitable candidate for a role in the Sinestro Corps. Having someone with force powers join up would be very interesting for the Sinestro Corps. A dominant and powerful leader and incredibly adept combatant prior to wielding a power ring, one can only begin to imagine just how powerful and corrupt Darth Vader could become with the powers of a yellow ring in his possession.