X-Men Animated Series: Marvel's Hidden Universe

Before the Marvel Cinematic Universe, Marvel built an interconnected animated universe on television. This era began with "X-Men: The Animated Series" in 1992, captivating audiences with its memorable theme song and serving as a gateway to the expansive Marvel Comics world for many.

The series not only focused on the titular X-Men but also incorporated guest appearances from a variety of Marvel Comics characters. While some, like Carol Danvers, were integral to character backstories, others made fleeting cameos, offering exciting glimpses for avid fans and perhaps appearing strangely to general audiences. This strategy successfully made the show feel like a window into a larger, shared Marvel universe.