Rocket Raccoon is one of the many test subjects that the High Evolutionary used to seek the perfect living being. However, Rocket is unique in that he's smarter than any of the High Evolutionary's other creations. Rocket Raccoon helped the High Evolutionary create the human-animal hybrids that populated Counter-Earth and designed a makeshift key to break out of his enclosure, after which he devoted his time to bounty-hunting, gadget creation (including Nebula's new high-tech arm), and an unexpected superhero career. While Rocket Raccoon's heightened intellect seems to be a random phenomenon, it's also possible that it comes from a mutation.
Deadpool Showed That Physical Trauma Can Cause The X-Gene To Activate
Reddit user BlindEditor draws parallels between Rocket Raccoon and Deadpool's origin stories. The Deadpool movies explain that the treatment Wade Wilson went through to cure his cancer awakened his dormant X-gene. In 2016's Deadpool, Francis a.k.a. Ajax explicitly told Wade Wilson, "I'm injecting you with a serum that activates any mutant genes lurking in your DNA. For it to work we need to subject you to extreme stress.". In Deadpool's case, a short time in an oxygen deprivation tank allowed him to develop an extreme healing factor that made him practically immortal. Technically, when a mutation is triggered artificially, the character is called a "mutate", but the set of abilities a mutate receives is roughly the same as if they had become a mutant naturally.
