10) Martian Manhunter
Martian Manhunter’s importance in the Justice League shouldn’t be understated. From the team’s inception in 1960 until The New 52 reboot came along in 2011, the last Martian was presented as one of the team’s founding members and a hero who had served on various variations of the League over the years. In The New 52, however, Cyborg was bumped up to founding member in his place and J’onn J’onzz’s significance was lessened.
Old-school DC fans will always see Martian Manhunter as a top tier member of the Justice League, though, so it would be great if the character could still find a way to turn up in the movie, even if he isn’t actually joining the team. One way that he could appear is by taking the form of a human character to aid the League in disguise, before the character unveils his true nature in a future movie. There’s even a precedent for this, as many fans believed that Harry Lennix’s General Swanwick in Man of Steel was really the Martian.