The High Evolutionary
In the MCU, Rocket Racoon was created by The High Evolutionary, as evidenced in The Guardians of the Galaxy: Vol 3 (released May 2023).
img src: https://www.looper.com/img/gallery/guardians-3-how-the-high-evolutionary-is-different-from-the-comics/intro-1683216244.jpg
During the events of Vol 3, the Guardians are attacked on their new base, Knowhere, where Rocket is
mortally wounded by Adam Warlock.
Setting off a chain of events where Rocket's in-built tracking and
kill switch
mechanism are triggered.
It was Nebula who interfaces digitally to Rocket's vital functions and accesses his in-built database and discovers a digital signature belonging to "OrgoCorp" as well as a need for a 'keyphrase' (which becomes the Maguffin and plot driver for the story).
The Guardians embark on a mission to determine the origin and creators of Rocket, which leads them to the the discovery of the High Evolutionary and his experiments in OrgoCorp, where he claimed:
I'm not trying to conquer the universe. I'm perfecting it.
During the course of the movie, we experience multiple 'flashbacks' of Rocket's early life (including from before his experiment) where he interacts with the High Evolutionary.
Fun fact: during the experiments, Rocket was designated the label "89P13" ('89' signifying the 89th batch of experiments).