Seven of the most formidable heroes form arguably the most powerful team ever.

Forces of evil, chaos, and destruction await. Not even protectors like Superman, Batman, Wonder Woman, Green Lantern, the Flash, Hawkgirl or the Martian Manhunter may have a chance alone. But together as the Justice League, they are a metahuman force (and a hope) to be reckoned with.

Season one settled the origin of the team. In the first episode, Batman and Superman banded together to stop an alien invasion. After freeing the last surviving Martian, and escaping from the aliens, they met four other superheroes – Hawkgirl, the Green Lantern, the Flash and Wonder Woman. After they took down the aliens, Superman decided that they should all stay as a force for good. This season didn't feature deep character development, unlike future seasons.

Season two was renamed Justice League Unlimited. The Justice League now had a new Watchtower, new Javelins, and a new roster. The original plan for the third and subsequent seasons was to have one core member leading a team of two or three new members on a mission.

Season three brought the conclusion of the Cadmus arc that brew in the former seasons. The season ended with a revelation that would change Terry McGinnis and Bruce's relationship forever. This season was meant to be the final one, but Cartoon Network called for a whole other season.

In season four, the Justice League had to face Gorilla Grodd's new Secret Society (also known as The Legion of Doom off screen.) Almost every villain the League ever faced was in this Society. At one point, Lex Luthor takes over control of the organization and uses its resources to try to free Brainiac, so that he can have ultimate knowledge again.