Cameo appearances were originally planned for Wolverine (James "Logan" Howlett) and Magneto (Erik Lehnsherr), who were present during World War II. At that time, Logan was a soldier and Lehnsherr was in an internment camp. However, these cameos were scrapped due to rights issues. As a result of the Disney-Fox merger of 2019, Marvel Studios now owns the rights to the X-Men characters.
Chris Evans declined the role of Captain America three times before finally accepting it. Not out of dislike for the role, but because he feared how the sudden increase of fame would affect his private life. Then Robert Downey Jr. convinced him to take the part, and thus gain the freedom to sign on any other role he'd want afterwards. After that, Evans had a meeting with director Joe Johnston and the producers, who convinced him to take the role. Evans reflected, "It was the best decision I've ever made, and I really owe that to Kevin Feige for being persistent and helping me avoid making a giant mistake. To be honest, all the things that I was fearing never really came to fruition."
Hayley Atwell based her performance as Peggy Carter on Ginger Rogers: "She can do everything Captain America can do, but backwards, and in high heels."
Stanley Tucci took the role of Dr. Erskine because the role enabled him to use a German accent, which he always wanted to do.
H.Y.D.R.A.'s futurist aircraft take their designs from actual World War II German concepts such as the Horten H.XVIII flying wing bomber and Triebflügeljäger fighter plane.