Avengers: Infinity War

Tony Stark / Iron Man: The benefactor of the Avengers who is a self-described genius, billionaire, playboy, and philanthropist with electromechanical suits of armor of his own making. Co-director Joe Russo explained that Stark "senses this greater threat approaching, so he is doing everything in his power to keep the Earth safe". Downey added that Stark has smaller goals than in previous films.

Robert Downey Jr.

Thor: An Avenger and the king of Asgard, based on the Norse mythological deity of the same name. Joe Russo stated that Thor's storyline picks up after the events of Thor: Ragnarok (2017), which finds him in a "very profound", "very interesting place" with "real emotional motivation". At the recommendation of Hemsworth, writers Christopher Markus and Stephen McFeely consulted Thor: Ragnarok director Taika Waititi and screenwriter Eric Pearson to help carry over the comedic and tragic elements of the re-toned Thor from that film. Joe Russo said that Thor has "the driving hero's arc of the movie which stands in direct opposition to Thanos' argument" and would have been the main protagonist of the film had Thor killed Thanos.

Chris Hemsworth

Bruce Banner / Hulk: An Avenger and genius scientist who, because of exposure to gamma radiation, typically transforms into a monster when enraged or agitated. Banner spends the film trying to reintegrate with the Avengers and "impress upon everybody how dangerous Thanos is". Joe Russo felt the Hulk refusing to appear for much of the film was only partially because he was scared, but also because he realizes that "Banner only wants Hulk for fighting. I think he's had enough of saving Banner's ass". Russo added that this was "really reflective of the journey from Ragnarok [...] [where] these two characters are constantly in conflict with each other over control". Banner's appearance in the film continues a story arc for the character that was established in Thor: Ragnarok and concludes in Avengers: Endgame (2019), with the difference between Hulk and Banner "starting to blur a little bit". Ruffalo described Hulk in Infinity War as having the mental capacity of a five-year-old.

Steve Rogers / Captain America: The fugitive leader of the non-regulation faction of Avengers. A World War II veteran, he was enhanced to the peak of human physicality by an experimental serum and frozen in suspended animation before waking up in the modern world. Joe Russo said after the events of Captain America: Civil War (2016), Rogers struggles with the conflict between his responsibility to himself and his responsibility to others. The character embodies the "spirit" of the comic book identity Nomad in the film, and receives new vibranium gauntlets from Shuri to replace his old shield. An early draft of the film had Rogers first appearing at the end of the film to save Vision from Corvus Glaive in Wakanda. Markus and McFeely were called "insane" for waiting that long to introduce Rogers into the film and ultimately conceded it was "not [a] satisfying" approach.

Chris Evans

Natasha Romanoff / Black Widow: A highly trained spy, member of Rogers' faction of Avengers, and former agent of S.H.I.E.L.D. Johansson said that Romanoff's situation following Captain America: Civil War has been "a dark time. I wouldn't say that my character has been particularly hopeful, but I think she's hardened even more than she probably was before."

Scarlett Johansson

Dr. Stephen Strange: A former neurosurgeon who, after a car accident that led to a journey of healing, discovered the hidden world of magic and alternate dimensions and became a Master of the Mystic Arts. Markus and McFeely described Strange as "[ending] up being the reasonable adult in the room" with the "widest perspective available". Julian "JayFunk" Daniels once again assisted Cumberbatch with his finger-tutting movements.

James "Rhodey" Rhodes / War Machine: An officer in the U.S. Air Force and Avenger who operates the War Machine armor. Following his paralysis during the events of Civil War, Rhodes is given an apparatus by Stark to walk again, although he is reluctant to don his War Machine armor and rejoin the Avengers due to his injury. Cheadle believed that Rhodes is "negotiating this reunion and his rejoining this team". He also explained that Rhodes' relationship with Stark "deepened" from his accident, saying, "I think Tony feels somewhat responsible and culpable in a way. But again, he's always had my back in a way that only he could really have".

Don Cheadle

Peter Parker / Spider-Man: A teenager, Avenger and Stark's protégé who received spider-like abilities after being bitten by a radioactive spider. Downey helped coach Holland through his death scene, which was not as drawn out in the script.

T'Challa / Black Panther: The king of the African nation of Wakanda who gained his enhanced abilities by ingesting the Heart-Shaped Herb. Boseman, along with the other actors from Black Panther (2018) portraying Wakandans, improvised their war chants on set ahead of the battle in Wakanda. Despite both Black Panther and Infinity War filming at the same time, the Russos were not aware of the chants, as they had not yet seen footage from Black Panther, and felt the moment was "incredibly cool".

Chadwick Boseman

Vision: An android and Avenger created using the artificial intelligence J.A.R.V.I.S., Ultron, and the Mind Stone. Anthony Russo called Vision "a living MacGuffin"; his life being in direct conflict with Thanos' quest, which "raises the stakes".

Wanda Maximoff: A member of Rogers' faction of Avengers who can harness magic and engage in hypnosis and telekinesis.

Elizabeth Olsen