<Li> Vin Diesel as Groot: A tree - like humanoid who is the accomplice of Rocket . Diesel stated that he provided the voice and motion capture for Groot, after originally being in talks to star in a new Phase Three Marvel film . Diesel also provided Groot's voice for several foreign - language releases of the film . Krystian Godlewski portrayed the character on set, though his acting was not used in the final character CGI . On the character, which Gunn based on his dog, Gunn said, "All the Guardians start out the movie as bastards--except Groot . He's an innocent . He's a hundred percent deadly and a hundred percent sweet . He's caught up in Rocket's life, really ." Gunn added that the design and movement of Groot took "the better part of a year" to create . Gunn added, "The ways in which Vin Diesel says,' I am Groot,' I am astounded . All of the' I am Groots' that were earlier voices didn't sound very good at all...Vin came in and in one day, laid down all these' I am Groot' tracks, and he's a perfectionist . He made me explain to him with ever (sic)' I am Groot,' exactly what he was saying...It was amazing when we first put that voice in there how much the character changed and how much he influenced the character ." Regarding the limited words used by Groot, Diesel said in many ways this was, "...the most challenging thing to ask an actor to do ." Diesel found an emotional note in his performance, invoking the death of his friend and Fast and Furious co-star Paul Walker, saying, "This was in December (2013), and the first time I came back to dealing with human beings after dealing with death, so playing a character who celebrates life in the way Groot does was very nice ." Groot's form and size - changing abilities are seen, with Gunn stating that he has the ability to grow in the film . </Li> <Li> Bradley Cooper as Rocket: A genetically engineered raccoon - like bounty hunter and mercenary who is a master of weapons and battle tactics . Gunn worked with live raccoons to get the correct feel for the character, and to make sure it was "not a cartoon character", saying, "It's not Bugs Bunny in the middle of the Avengers, it's a real, little, somewhat mangled beast that's alone . There's no one else in the universe quite like him, he's been created by these guys to be a mean - ass fighting machine ." Gunn also based the character on himself . Describing Rocket in relation to the rest of the Guardians, Cooper said, "I think Rocket is dynamic . He's the sort of Joe Pesci in Goodfellas guy ." Cooper voiced Rocket, while Sean Gunn (James' younger brother) stood in for the character during filming . James Gunn said that for the role of Rocket, some physical movement from Cooper, including facial expressions and hand movements, was recorded as potential reference for the animators, though much of Sean Gunn's acting is used throughout the film . Before Cooper was cast, James Gunn said that it was a challenge finding a voice for Rocket, that he was looking for someone that could balance "the fast - talking speech patterns that Rocket has, but also can be funny, because he is really funny . But also has the heart that Rocket has . Because there are actually some pretty dramatic scenes with Rocket ." </Li> <Li> Lee Pace as Ronan the Accuser: A Kree radical who agrees to retrieve an artifact for Thanos in exchange for eradicating his mortal enemies, the Xandarians . Ronan and his Sakaaran army hunt down the Guardians when they interfere with his goals . Describing Ronan, Gunn said, "He is the primary villain, and he is a really twisted guy, he has a really religious bent in this film . He has a very sick and twisted view of what morality is; strength is virtue and weakness is sin and that is what he lives by, and I think he is very scary because of his beliefs, which are real to him ." Pace, who originally auditioned for Peter Quill, described Ronan as a "psycho" and a "monster". </Li> <Li> Michael Rooker as Yondu Udonta: A blue - skinned bandit who is the leader of the Ravagers and a paternal figure to Quill . Yondu helps Quill to steal the orb before Quill betrays him, leaving Yondu and the Ravagers to chase the Guardians . On the character, Rooker said, he has "some interesting issues--not a good guy, not a bad guy . There's hope and there's a heart inside Yondu ." Gunn created the film's version of the character specifically with Rooker in mind, while borrowing the character's mohawk and use of a whistle - controlled arrow from the comics . Rooker fully committed to the role once he knew his role on the TV series The Walking Dead would be ending . Rooker's makeup took approximately four hours to apply . </Li>

Who plays ronin on guardians of the galaxy