The first Justice League movie had an unlikely origin.
The 1989 success of Batman had Warner Brothers looking to develop more DC properties for the big and small screen. The first of these efforts was the 1990 television series, The Flash. While short lived, the series had been well received by fans. One of the problems with the series was that the same special effects that were lauded by critics and fans made the cost per episode prohibitive for the modest viewership of the series.
Shortly after the series cancellation, however, proponents of the now defunct series started to try pitching have an appearance for John Wesley Shipp's Flash in the next Batman movie, citing Burton's Batman as a big influence on The Flash.
While the discussions for an appearance of the Flash in Batman Returns weren't successful, it did spark discussions at Warner Brothers about a possible DC superhero team-up movie.
Batman Returns was critically acclaimed (one critic going so far as to call it 'possibly the first blockbuster art film') but was somewhat controversial as it was felt to have gone 'too adult' for a movie based on a comic book superhero. It made good box office, but it was felt at Warner Brothers that it should have done better. Executives started discussions about going with a different director and a lighter script for a third Batman film, and once again the idea of a superhero team-up with The Flash was raised. However, things took an interesting turn when someone brought up that Warner Brothers had just acquired the movie rights for Superman, and that Christopher Reeve had been considering a return to the role. And that is how the first idea of a Justice League movie was born.
Once plans began to explore the possibility of a Justice League movie, especially one that might star the most recent actors to have played the roles of Batman, The Flash, and Superman, thoughts naturally turned to what should be the premise, and who should the play the other members of the League, especially the role of Wonder Woman. At the same time, word from on high in Warner Brothers was that the front office wanted to relaunch the DC universe. By that time, the creative team had become excited about a potential for a match-up of the actors of the past decade to bring these characters to life, but realized that to sell their use, there would have to be some way to at the same time use the movie as a springboard to a new future DC franchise for Warner Brothers. The answer was to turn to the largest DC comics event of the 1980s - Crisis on Infinite Earths. The idea would be to use the premise of superheroes from multiple earths coming together to fight for all of existence, but that the outcome would be a whole new universe (and thus new opportunities to launch the origin stories of all the DC properties owned by Warner Brothers.
Once the premise of Crisis on Infinite Earths had been forwarded, it was felt that the creative team had more latitude on what they could do in the Justice League movie, since the climax would see the entire DC universe 'reset'. With Michael Keaton, John Wesley Shipp, and Christopher Reeve all planned to reprise their superhero roles, the idea was floated to bring back the actress most people still thought of as Wonder Woman for the movie, Lynda Carter. Even though it had been almost 20 years since her first portrayal of the Amazonian, she was still a very active and attractive woman, and it was felt that her return in Justice League would be fitting way to complete the last era of television and film superheroes.
