season of Justice League (which in turn built upon events in Batman: The Animated Series, Superman: The Animated Series, Batman Beyond, Static Shock, and The Zeta Project), and would go on to affect the plotlines of most of its episodes. It was resolved in a four-part story at the end of the second season of Justice League Unlimited. The third and final season story arc focuses on the new Secret Society (which is based on the Legion of Doom of the Challenge of the Super Friends season of Super Friends), a loose-knit organization formed to combat the increased superhero coordination of the first season. While the Secret Society is never referred to as the Legion of Doom, there were early plans to use the name (coined in typically comedic style by the Flash). The idea was rejected. The series, along with the entire DC animated universe, was originally planned to end after the second-season finale "Epilogue", but a third season was greenlit by Cartoon Network. The third season started in 2005 with the episode "I Am Legion" (which was written before the announcement of a third season) and ended in 2006 with the episode "Destroyer". According to Matt Wayne, if the show had been renewed for a fourth season, he would have liked to write more episodes focusing on Superman and Wonder Woman. Towards the end of the series, certain characters became off-limits to the show, like Blue Beetle and Hugo Strange. Characters associated with Batman and those who appeared in Batman: The Animated Series (aside from Batman himself) were restricted due to the unrelated animated series The Batman and Christopher Nolan's live-action The Dark Knight Trilogy, in order to avoid continuity confusion (although the villain the Clock King did make an appearance, he appeared as a member of Task Force X and did not interact with Batman). Aquaman and related characters were unavailable due to the development of a pilot for a live-action series featuring the character as a young man (planned to be a spin-off of Smallville). Characters from DC's "mature readers" Vertigo imprint were also not allowed, such as Swamp Thing and Phantom Stranger. No characters from the Teen Titans animated series appeared in JLU until after that show had been canceled (when Speedy appeared in the third-season episode "Patriot Act", which referenced the Seven Soldiers of Victory). While The Joker, Batman's archenemy, had appeared in the