7. Sinestro
Sinestro is of course the arch nemesis of Green Lantern and the former mentor of Hal Jordan. He famously turned against the Guardians of the Universe and established his own Sinestro Corps to spread fear throughout the universe. Sinestro actually has a pretty great origin story that would make for an interesting film, and perhaps showing his training of Hal and eventual mutinous actions could be incorporated as well. He was born on the planet Korugar, and worked as an anthropologist who specialized in preserving and reconstructing the ruins of long-dead civilizations. One day on the job, a Green Lantern named Prohl Gosgotha crash-lands at the excavation site and gives his ring to Sinestro. Sinestro manages to defeat the being chasing Gosgatha, who it turns out isn't dead yet. Gosgatha asks for the ring back to keep him alive long enough to get help, but Sinestro allows him to die so that he can remain a Lantern. Sinestro is a character completely devoted to order, so much in fact that he feels the only way to maintain that order is to rule with an iron-fist. That kind of motivation, and how it consumes him to becoming one of DC's best villains, is ripe for exploration.