And though Joe and Anthony Russo took the reins in charting this character's adventure, it was Guardians director James Gunn who had a major influence on Groot's appearance in the new movie, according to senior visual development artist Anthony Francisco.
"James Gunn also wanted to add a bit of an ungroomed attitude where he does not clean up after himself, like trimming his greenery in those awkward spaces and adding a little belly to show him not caring about his appearance," Francisco told The Art of Avengers: Infinity War.
As an executive producer on the new movie, Gunn had a lot of influence over the direction of the Guardians in Avengers: Infinity War, and not just with the characters' appearances. Infinity War co-writer Christopher Markus spoke about how James Gunn affected the film's story.
"James' contributions were primarily voice-related, to make sure that we are not rolling out people who bear no resemblance to people in the preceding Guardians movies," Markus said to The Hollywood Reporter. "He was on board everywhere we were taking them. He adjusted one choice in the movie that didn't really affect how the movie played, but it affected character a little bit. It was a very interesting choice, and first we wavered on it, and then [Guardians star Chris] Pratt backed him up. And we acknowledged, if anyone knows these characters, it's them."
Co-writer Stephen McFeely addressed how Infinity War brought in many popular Marvel characters from different franchises, including Black Panther and Doctor Strange, and how they were able to lean on the filmmakers for guidance.
"That's the benefit of all of this. The filmmakers who spent a lot of time with these characters get to come in and help us make sure we are getting it letter perfect," McFeely said. "There are 23 people on that poster, so there are going to be people who are slightly more expert at those characters than we are. So, we did that with everybody. [Doctor Strange director Scott] Derrickson and [Black Panther director Ryan] Coogler and [Thor: Ragnarok director] Taika [Waititi] and [Ant-Man director] Peyton Reed."
We'll see how those directors' influences extend into the future when Avengers 4 premieres in theaters on May 3.