<Li> Zoe Saldana as Gamora: A member of the Guardians, who is an orphan from an alien world and raised by Thanos, seeking redemption for her past crimes . Ariana Greenblatt portrays a young Gamora . </Li> <Li> Vin Diesel as Groot: A member of the Guardians who is a tree - like humanoid . Executive producer James Gunn explained that Groot is still an adolescent in the film, in the same state of growth seen in one of the post-credit scenes in Guardians of the Galaxy Vol. 2 . Terry Notary provided motion capture for Groot, and said the character is "coming of age, so you'll see the teenager find a mentor to look up to and to model himself after". </Li> <Li> Bradley Cooper as Rocket: A member of the Guardians who is a genetically - engineered raccoon - based bounty hunter and mercenary, and is a master of weapons and battle tactics . Sean Gunn was again the stand - in for Rocket during filming, with his acting and expressions serving as motion reference for the character . </Li> <Li> Gwyneth Paltrow as Pepper Potts: Stark's fiancée and the CEO of Stark Industries . Downey felt that "Pepper remains the heart of the (Iron Man) story", which was not a focal point in some of the preceding films with Stark . Downey continued that "we wanted to get back to that reality . Not just for them, but let's really see how that can add to the something - worth - fighting - for of it all ." </Li>

What is the avengers infinity war movie about