Captain America

Captain America was a superhero. According to some accounts, Captain America was fictional (TV: The Return of Doctor Mysterio, COMIC: Moving In) but according to others, he was a real individual existed in Earth-616 (COMIC: Camelot Lost) Earth-33⅓, (COMIC: Doctor Who? 64) and Earth-238. (COMIC: Waiting for the End of the World)

Biography
Captain Britain recalled fighting alongside Captain America, referring to him as one of "the world's greatest heroes". (COMIC: Camelot Lost)

Other references
Captain America was a "skinny little guy" who later became a hero. The Twelfth Doctor claimed this showed how being a hero could happen to anyone. One of the villains fought by Captain America was the Red Skull. The Doctor believed all he needed to win in a fight with Batman was his shield and his wits. Maxwell Collins argued that Batman would win instead. (COMIC: Moving In)

Grant had a poster of Captain America on the door of his childhood bedroom, as well as another poster next to the window depicting him next to Wolverine. (TV: The Return of Doctor Mysterio)

Earth-33⅓
A version of Captain America existed in Earth-33⅓. In this universe, once entered the Doctor's TARDIS, along with Superman, Batman, Spider-Man, and Jet Lagg when the Fifth Doctor landed it in New York during a crimewave. (COMIC: Doctor Who? 64)

Earth-238
On Earth-238, Captain America was among the superheroes taken to death camps. (COMIC: Waiting for the End of the World)

Behind the scenes
Multiple DWU actors have played roles in the Captain America film series:
 * David Bradley played the tower keeper in the 2011 film Captain America: The First Avenger.
 * Michael Brandon played Senator Brandt in The First Avenger.
 * Jenna-Louise Coleman (as she was then credited) played Connie in The First Avenger.
 * JJ Feild played James Montgomery Falsworth in The First Avenger.
 * Sophie Colquhoun played Bonnie in The First Avenger.
 * Hayley Atwell played Peggy Carter in The First Avenger and the 2014 film Captain America: The Winter Soldier.
 * Toby Jones played Dr Arnim Zola in The First Avenger and The Winter Soldier.
 * Jenny Agutter and Alan Dale played members of the SHIELD council in The Winter Soldier.