7. Krona
DC ComicsIf DC want to go really big and have the Green Lanterns go up against a truly universal threat - and we're talking Galactus level or Thanos with the Infinity Gauntlet level here - then they could bring the cosmic monster that is Krona to the big screen. Krona was an Oan scientist (Oa being the home of the Green Lanterns and the Guardians of the Universe), but he became something more thanks to his exploration of the universe's origins - a deed that would result in a complex backstory for the character. Despite being warned that the consequences could be devastating, Krona constructed a machine that pierced the temporal barrier and he got to witness the beginnings of time itself. He caught a glimpse of the hand of creation itself depositing the first atom that would become the entire cosmos. At that moment, his machine exploded and created the multiverse itself, as well as a number of parallel universes - including the Anti-Matter universe, which unleashed evil in to the cosmos. Subsequently, Krona was responsible for the creation of the abstract entities the Monitor and the Anti-Monitor. As a punishment for his actions, Krona was transformed into pure energy by his fellow Oans and condemned to wander the universe in a formless state. He tries to gain form again - and tries to destroy the Guardians and the Green Lanterns - but is defeated. His universal schemes would create an unprecedented level of threat in a DC movie and that would be pretty cool.