Captain Universe is a character appearing in American comic books published by Marvel Comics. Created by Bill Mantlo and Michael Golden, the character first appeared in Micronauts #8 (August 1979). Captain Universe is the guardian and protector of Eternity. Rather than a character with a single identity, it is a persona that has merged with several hosts during its publication history.

Captain Universe first appeared in Micronauts #8 (August 1979) and was created by Bill Mantlo and Michael Golden.

Captain Universe hosts have appeared in either special one-shots or short stories throughout the years, initially in the first series of the Micronauts in 1979.

Captain Universe was the starring feature in issues #9–11 of the tryout series Marvel Spotlight. The series' editor Al Milgrom recalled being taken away by the concept of a Captain Universe serial: "You could come up with three issues, three disparate individuals — each one very different from the other — and see how they use their powers. They wouldn't necessarily be superheroic types; they'd be regular people who fell into the powers for just one issue. ... But Captain Universe never got his own title, so I'm guessing it didn't sell terribly well." The character appeared sporadically through the remainder of the 1980s in titles such as Marvel Fanfare and Contest of Champions.

His appearances became even scarcer in the 1990s, appearing in Guardians of the Galaxy, What If?, The Amazing Spider-Man, Marvel Comics Presents and Cosmic Powers Unlimited.

In 1994, Captain Universe appeared in a one-shot, coinciding with a promotion, with the claim that readers could have a comic about themselves made for a fee. The comics were generally stock stories, with minor details altered based on information provided by the purchaser. Jeff Christiansen, then a veterinary student and who would later become the force behind the resurgence of the Official Handbook of the Marvel Universe in the mid-2000s, was written and drawn as the official Captain Universe of the comic so that it could be considered an in-continuity comic. The one-shot was titled X-Men/Captain Universe: Sleeping Giants.

In 2005, after a four-year break from comic appearances, Captain Universe returned in the second series of Amazing Fantasy. Also in 2005, a series of one-shot specials were released featuring different characters from the Marvel Universe as the Uni-Power each imbues them with power of Captain Universe. These titles were Captain Universe/Hulk, Captain Universe/Daredevil, Captain Universe/X-23, Captain Universe/Invisible Woman and Captain Universe/Silver Surfer. The Uni-Power made a brief appearance in Nextwave, he also made a "cameo" as Cosmic Spider-Man for the variant cover of Friendly Neighborhood Spider-Man #3 and played an important part in the Death's Head 3.0 saga chronicled in Amazing Fantasy.

Captain Universe made his return in Annihilation: Conquest: Star-Lord and then in Annihilation Conquest #3. Captain Universe later returns to stop the Juggernaut, in an attempt to fulfill his destiny, as seen in The Amazing Spider-Man #627–629.