The Guardians of the Galaxy are a spacefaring team of superheroes consisting of humans and aliens that has been around for a decade as an official team and for more than a decade before as a band of heroes. Whose self-declared mandate is to protect the universe from any threats, usually those that are galactic-level threats or higher. They've fought a variety of entities, organizations, races, empires, armies, and fleets including the Brood and Phalanx. It's the Badoon and the Universal Church of Truth whom are their mortal foes.
They played a decisive role in the conflict with the Cancerverse, the reality conquered by the Old Ones. Which first infiltrated the prime reality and then launched an invasion to conquer the universe. The Guardians of the Galaxy first investigated the Cancerverse and once war erupted, they acted as a strike force by entering the alternate universe and crippling the invasion thereby saving the prime reality. Afterwards they would continue to have dealings with the Cancerverse.