Shorty after the release of Guardians of the Galaxy (2014), Marvel announced its sequel, slated for release on July 28, 2017. So, in the year following the film's unexpected success, fan theories have circulated as to what the Guardians of the Galaxy sequel will entail. One such theory is a crossover film involving the Guardians characters and The Incredible Hulk. 

During Guardians of the Galaxy’s early development stages, it was intended for the Badoons, a reptilian alien race in the Marvel Comics universe, to serve as one of the film's many antagonists. However, the Badoons film rights belong to 20th Century Fox rather than Walt Disney Studios Motion Pictures, and the latter were responsible for distributing Guardians of the Galaxy. Therefore, the Sakaarans, a humanoid race, were chosen to take their place.

Ruled over by the Red King and divided into two ethnic groups, the ruling class of red-skinned Imperials, and the nomadic grey-skinned shadow people, the Sakaarans appropriately inhabit the planet of Sakaar, which also serves as the primary setting in the Planet Hulk storyline that ran through issues of "The Incredible Hulk" comic from April 2006 to June 2007.

Within those comic issues, the story tells that after S.H.I.E.L.D. decides the Hulk is too dangerous to remain on Earth, they devise a plan to transport him to a world where there is no sentient life and he cannot harm to anyone. Instead of that plan coming to fruition, the Hulk finds himself on the planet of Sakaar, where he and other gladiators are drafted for the Red King’s amusement. Eventually, a rebellion ensues, which de-thrones the emperor-like villain and Hulk leaves the shattered planet to return to Earth.  

Actor Mark Ruffalo, who portrayed Bruce Banner and his alter-ego in The Avengers (2012) and Avengers: Age of Ultron (2015), as well as many others have expressed interest in seeing this storyline on the big screen, yet there is serious doubt it will ever actually be told.

Once again, due to film rights, only one stand-alone Hulk film was allowed. This was of course The Incredible Hulk (2008), which stared Edward Norton as the eponymous hero. All of the Hulk’s film appearances since have been as a side character in the Avengers franchise. Plus, Guardians of the Galaxy director James Gunn has stated that all rumors in regards to Guardians of the Galaxy and Incredible Hulk appearing together are completely false. 

At the very least, the Sakaarans’ appearance in Guardians of the Galaxy serves as a nice little Easter egg for all Marvel nerds. The fact that their presence could potentially set the stage for a crossover between the assorted group of intergalactic criminals and the Avengers scene stealer is still fun to think about and hope for.