In the first Guardians of the Galaxy movie, it is established that Rocket Raccoon has a pretty nasty backstory, having been “torn apart and put back together over and over and turned into some little monster”although details about the experiments that turned him into the gun-toting mercenary we all know and love are kept vague. However, according to James Gunn, Rocket’s origin will be explored in an upcoming Marvel movie.
“As you know, the MCU is one way of processing these characters,” said Gunn at Hascon (via MCU Exchange). “616 is a different one. We are going to learn more about where Rocket comes from in the coming sagas. It’s going to be a little different from the comics. We already know a lot about from where he came from. It’s a little bit more horrible than what it is in the comics when you come down to it. We will learn more about that.”
One would imagine there’ll be way too much going on in Avengers: Infinity War to delve into Rocket’s origin, so Gunn is presumably be referring to Guardians of the Galaxy Vol. 3, or a future cosmic Marvel movie. Perhaps even that rumoured Rocket and Groot solo movie?