The Season 4 premiere of "X-Men: The Animated Series" saw the unstoppable powerhouse, the Juggernaut, hunting down his half-brother, Professor Charles Xavier. With the X-Men away from the Xavier Mansion, Charles had to concoct another strategy to stop the Juggernaut. One of these training modules involved a robotic version of the Hulk, who attacked the Juggernaut in a desert environment. The Hulk's cameo on "X-Men: The Animated Series" is noteworthy because his presence in a Danger Room training module suggests the mutant superhero team had crossed paths with him at some point in the past. The year after "The Juggernaut Returns" aired, the Hulk would land his own animated series set in Marvel's animated universe, meaning his "X-Men" cameo was technically the first appearance of this version of the character.