Deuteragonist / Marvel Cinematic Universe

Marvel Studios - The Infinity Saga

As a whole (or at least in the Infinity Saga), either Steve Rogers or Tony Stark could be considered the deuteragonist to the other's protagonist ^note  The argument for Steve being the protagonist is that he is chronologically the first superhero in the MCU, is The Leader and has the most screen-time in both Avengers films and his standalone films are more plot-critical to the MCU as a whole than those of the other Avengers' more self-contained narratives. Tony's is that his film was the first in the series, he undergoes the most Character Development across both his own films and the Avengers, he is a major character even in other characters films, his presence (along with his family's) influences many of the films he doesn't appear in and he is ultimately the one to land the finishing blow on Thanos in the Grand Finale of the movie. while Thor is the undisputed tritagonist due to being the only other original Avengers member with his own film trilogy and having several elements of his films be vital pieces of the overall Myth Arc. Within the individual series, we have these:

Phase One

• Iron Man has Pepper Potts, Tony Stark's assistant and love interest, with James Rhodes serving as the tritagonist.
• The Incredible Hulk has Betty Ross, Bruce Banner's love interest and the daughter of the man most set on catching Banner.
• Iron Man 2: James Rhodes - now becoming the War Machine - assumes the deuteragonist role, with Pepper Potts as the tritagonist.
• Thor The titular character love interest Jane Foster having the primary point of view in that film, with Darcy Lewis and Erik Selvig as the tritagonists.
• Captain America: The First Avenger has Peggy Carter, Steve's love interest and one of the original founders of S.H.I.E.L.D., with Bucky Barnes, Steve's best friend as the tritagonist.
• The Avengers: The six original Avengers share the protagonist role, leaving Nick Fury as the deuteragonist and Phil Coulson as the tritagonist.

Phase Two

• Iron Man 3: Rhodes and Pepper share the deuteragonist role, with the former becoming the face of US government wich is very important for the plot and the latter has most personal connection with the story.
• Thor: The Dark World: Jane Foster remains as the deuteragonist, with Loki is now the anti-heroic tritagonist.
• Captain America: The Winter Soldier has Natasha Romanoff.
• Guardians of the Galaxy (2014): Even though it's a well rounded ensemble, Gamora is the deuteragonist and Drax is the tritagonist to Quill's protagonist. Gamora because she has more connection with the villains and is a possible love interest for Peter Quill. Drax because he is in a Roaring Rampage of Revenge against the villains responsible for killing his family and his Character Development revolves around that. Rocket Raccoon, Groot and Yondu are mostly supporting characters.
• Avengers: Age of Ultron: The six originals remains as the protagonists, with the big bad former co-dragons Pietro and Wanda Maximoff pulling a Heel–Face Turn during the course of the movie and becoming the deuteragonists and the recently created Vision as the tritagonist.
• Ant-Man: Hank Pym; he's the original Ant Man and is the leader of the heroes. He has his own flashback story and the strongest connection to the villain. His daughter Hope van Dyne is being set up as the deuteragonist to Ant-Man in general, considering she gets title billing in the film's sequel, Ant-Man and the Wasp.

Phase Three

• Captain America: Civil War has Tony Stark.
• Doctor Strange (2016) has Karl Mordo as the film's deuteragonist since he has the second most amount of character development, he also gets the final scene after the credits
• Guardians of the Galaxy Vol. 2 : Rocket Raccoon is the deuteragonist. The movie has a Two Lines, No Waiting narrative and while the first one is about Quill, the second one is about Rocket. Gamora and Yondu are both tritagonists by virtue of being the second most important character in each of the two plots.
• Spider-Man: Homecoming:
• Thor: Ragnarok:
• Black Panther (2018): T'Challa is unquestionably the protagonist of the movie, but the story is also largely about Erik Killmonger, and much focus is placed on the differences between the two and how they ended up on such different paths. Frankly, Killmonger is deuteragonist, as opposed to being a co-protagonist, solely by virtue of being the Big Bad — especially since, from a certain point of view, The Bad Guy Wins.^note Though an Omnicidal Maniac, Killmonger also stands for the political viewpoint of inteventionism, believing that Wakanda, an Afro-futurist Crystal Spires and Togas nation with advanced technology, should be helping the world. (Or, at least, using that advanced technology to conduct a Full-Circle Revolution. He is an Omnicidal Maniac.) T'challa, on the other hand, is an isolationist, holding the same view as previous kings: that Wakanda should just let the world handle its own affairs. The final scenes of the film show that Killmonger's influence has made its mark, as T'challa takes a third option and has Wakanda begin Technology Uplift efforts with the rest of the world.
  • Avengers: Infinity War: despite being in the title, the Avengers are deuteragonists. This film belongs to Villain Protagonist Thanos — especially since The Bad Guy Wins, and it's not from a certain point of view.
• Ant-Man and the Wasp: Ava Starr (aka Ghost), the daughter of Hank Pym's former partner Elihas Starr and adopted daughter of another of his partners, Bill Foster, wants to heal her increasingly unstable intangibility by stealing Pym's quantum technology, while the significantly less competent Sonny Burch, learning of the technology from a mole in the FBI, also tries to steal it in order to sell it on the black market. Both of their attempts to steal the technology clash with Hank and Hope van Dyne, now the Wasp, going to Scott for help to rescue Janet van Dyne from the Quantum Realm.
• Captain Marvel: While this is most definitely first and foremost the Super Hero Origin of Carol Danvers, the film also tells the story of Nick Fury from before he ever becomes the Big Good to the Avengers and S.H.I.E.L.D.
• Avengers: Endgame:
• Spider-Man: Far From Home:

Marvel Studios - The Multiverse Saga

Phase Four

• WandaVision: As per the title, Wanda is the protagonist with Vision as the deuteragonist. The tritagonist is noisy neighbor Agnes, being the Hidden Villain Agatha Harkness.
• The Falcon and the Winter Soldier: Each episode tends to switch between Sam and Bucky as having the primary point of view, but in the series as a whole, Bucky is the deuteragonist to Sam's protagonist. John Walker is the tritagonist.
• Loki (Season 1):
• Black Widow: Yelena is the deuteragonist to Natasha's protagonist. Of their parents, Alexei has a slightly stronger case for being the tritagonist for the story as a whole, although Melina is crucial in the climax.
• What If...? (Season 1):
• Shang-Chi and the Legend of the Ten Rings: Katy is the deuteragonist. The tritagonist happens to be Big Bad Xu Wenwu, as the story places a great deal of importance on his past and how he became what he is during the events of the movie.
• Eternals:
• Hawkeye:
• Spider-Man: No Way Home: Michelle is the deuteragonist, having far more focus now as Peter's girlfriend. Either Ned or May could be considered a tritagonist given their importance to the story tho May's impact on it becomes posthumous halfway through. While crucial to the story, the alternate Peters are still strictly supporting players, even if Peter 3 does have a small character arc of his own.
• Moon Knight:
• Doctor Strange in the Multiverse of Madness: The sequel has America Chavez replacing Mordo as the deuteragonist with the main conflict of the story being Strange protecting her from Wanda.
• Ms. Marvel:
• Thor: Love and Thunder: Jane is the deuteragonist, being The Lancer. Valkyrie is the tritagonist.
• She-Hulk: Attorney at Law:
• Werewolf by Night:
• Black Panther: Wakanda Forever: Much like in the previous movie, Big Bad Namor is the deuteragonist to Shuri's protagonist, with the story being almost as much about him, his past and his people as it is about Shuri's. Several Wakandans (Nakia, Queen Ramonda, and Okoye particularly) have a strong case for being the tritagonist.
• The Guardians of the Galaxy Holiday Special:

Phase Five

• Ant-Man and the Wasp: Quantumania: Scott is the Pinball Protagonist. Cassie and Janet are the deuteragonist and tritagonist, but which of them is which depends on the story focus: Janet has the biggest connection to the antagonist, while Cassie acts as The Lancer to her dad and has perhaps the most prominent character arc in the movie. Despite being in the title and the deuteragonist of the previous movie, Hope is in a more supporting role (either to her mom or Scott) this time around.
• Guardians of the Galaxy Vol. 3: Much like in Volume 2, Rocket Raccoon and for similar reasons: Quill is the main character in the A plot while Rocket is the main character in the B plot. That said, Quill is a Supporting Protagonist this time as, unlike in Vol. 2, the overall story is about Rocket and not him. All the other guardians get sufficient screen time and plot relevance to be the tritagonist, but it can be argued that Mantis is the one who undergoes the most character development.