Baron Zemo is the name of two fictional characters, both supervillains, in various Marvel Comics comic books, notably Captain America and the Avengers. The original Baron Zemo was first seen in The Avengers #4 (March 1964); the second Baron Zemo first appeared in Captain America #168 (December 1973).

In 2009, Baron Helmut Zemo was ranked as IGN's 40th Greatest Comic Book Villain of All Time.

The original Baron Zemo was created by Stan Lee and Jack Kirby and was first seen in a flashback in The Avengers #4 (March 1964), though he did not actually appear in person and was not identified by name until The Avengers #6 (July 1964) and Sgt. Fury and His Howling Commandos #8 in the same month. Zemo was retroactively added into the history of Captain America upon the hero's reintroduction to the Silver Age two issues prior.

The character subsequently appears in The Avengers #7 (August 1964), #9-10 (October–November 1964), Tales of Suspense #60 (December 1964), and The Avengers #15 (April 1965), in which he is killed.

Captain America is a fictional character, a superhero who appears in comic books published by Marvel Comics. The character first appeared in Captain America Comics #1 (cover-dated March 1941), from Marvel Comics' 1940s predecessor, Timely Comics, and was created by Joe Simon and Jack Kirby. As of 2007, an estimated 210 million copies of "Captain America" comic books had been sold in 75 countries. For nearly all of the character's publication history, Captain America was the alter ego of Steve Rogers, a frail young man who was enhanced to the peak of human perfection by an experimental serum in order to aid the United States war effort. Captain America wears a costume that bears an American flag motif, and is armed with an indestructible shield that can be thrown as a weapon.

An intentionally patriotic creation who was often depicted fighting the Axis powers of World War II, Captain America was Timely Comics' most popular character during the wartime period. After the war ended, the character's popularity waned and he disappeared by the 1950s aside from an ill-fated revival in 1953. Captain America was reintroduced during the Silver Age of comics when he was revived from suspended animation by the superhero team the Avengers in The Avengers #4 (March 1964). Since then, Captain America has often led the team, as well as starring in his own series.