Captain America and the Winter Soldier

Sebastian Stan as James "Bucky" Barnes / Winter Soldier / White Wolf:

An enhanced soldier and Steve Rogers' best friend during the 1940s who was presumed killed in action during World War II, before re-emerging as a brainwashed assassin in the present day.[6][7]:4 Head writer Malcolm Spellman noted that Barnes has done "nothing but fight" in the last 100 years, and the series could not avoid the trauma that he has gone through.[8] Stan explained that Barnes would be struggling with his murderous past while also adjusting to life in the 21st century without Rogers,[9] and was having an identity crisis.[7]:4 Co-executive producer Zoie Nagelhout explained that Barnes would be working to "unburden himself" from his life as the Winter Soldier but the darker side of the character would still be seen during the series.[7]:5

Anthony Mackie as Sam Wilson / Falcon / Captain America:

An Avenger and a former pararescueman who was trained by the military in aerial combat using a specially designed wing pack.[6][7]:4 Wilson was handed Captain America's shield by Rogers at the end of Avengers: Endgame (2019),[4] and the series expands on this moment to explore the implications of a Black man being given that mantle.[10] Wilson initially continues to use the Falcon moniker in the series,[11] and Mackie said the story would portray the shield as being a burden for the character.[8] He added that Wilson is questioning how "a Black man [can] represent a country that does not represent him".[7]:2 Wilson eventually takes up the shield to become the new Captain America.[2]

Wyatt Russell as John Walker / Captain America / U.S. Agent:

A decorated member of the U.S. Military and the new Captain America was chosen by the U.S. government. He attempts to join Wilson and Barnes in their fight,[12][7]:5[13] and believes he is a better embodiment of American values than Rogers was.[8] After being stripped of the Captain America title, Walker is given the moniker U.S. Agent by Valentina Allegra de Fontaine.[2] Spellman described Walker as a soldier who has "done everything his country has ever asked" and is now faced with a reality where his life and sense of duty to the United States "challenge [him] in a way that upsets and obliterates [his] privilege".[14] Russell added that Walker was a "company man" who might venture into "the grey areas" to complete the mission.[15] He was attracted to the character's "dichotomies", and he had room to shape the character since this is his introduction to the MCU.[7]:5 Spellman said Walker was inspired by the comic book character, who uses the moniker U.S. Agent, but the series had shifted away from the comic book portrayal to add some different dimensions to this version.[16] Feige added that a White man, Russell, was specifically cast as the new Captain America as commentary on how the U.S. government would not want a Black man like Wilson to take on that role.[17]

Erin Kellyman as Karli Morgenthau:

The leader of the anti-patriotism group the Flag Smashers, who are enhanced with a recreation of the Super Soldier Serum and believe the world was better during the Blip, fighting for open national borders.[14] Spellman called Morgenthau "the glue for the series". Flag-Smasher in the comics is an identity assumed by male characters, notably Karl Morgenthau. Kellyman felt it was "important" the character was gender-swapped for the series, giving young women a character they could "look up to and relate to now". She added since Karli is not a middle-aged man like Karl, Karli's outlook on life and the actions she takes come from a different perspective.[18]