5. Captain America's shield is made of an alloy of steel and comic book super metal "vibranium," which makes it virtually indestructible. Over the years, it has withstood various death rays, bullets and even Wolverine's claws.
6. Speaking of the shield, Captain America's first shield wasn't round, but was similar to the type used by medieval knights (at least the Hollywood variety). It was later switched out for the circular version, which he can also throw.
7. Captain America's most famous partner/sidekick is James "Bucky" Barnes, an acrobatic and sharp-shooting teenager. Depending on different comic book histories, Bucky died during Captain America's last World War II mission, he survived and became the "Winter Soldier" or he escaped harm, married, settled down and met his old friend many years later.
8. Though Bucky was Captain America's first and most famous sidekick, he's also worked alongside The Falcon and Nomad.
9. Nick Fury, as played by Samuel L. Jackson, has figured into several of Marvel Comics movies (the "Iron Man" movies and "Thor"), but he's very different than the original comic book version.
In the original comics, Nick Fury, the director of S.H.I.E.L.D., was Sergeant Nick Fury, the leader of the Howling Commandoes, a group who fought alongside Captain America during World War II. He had the eye patch, but he wasn't black.
However, in the Ultimate line of Marvel comics, which the films heavily draw from in terms of style, Fury was reintroduced with a new background. The comic book character was also modeled directly on Samuel L. Jackson. In essence, for the movies, Jackson is playing a character he inspired.
10. In the comic books, Captain America was frozen in an icy, suspended animation for decades. Namor, the Submariner, discovered his body frozen in a block of ice, which was being revered by arctic tribesmen. Angered, the Submariner tossed the block into the sea where The Avengers later discovered it.
Bonus fun fact: "Captain America #1" was first published in 1940, a year before the bombing of Pearl Harbor and the United States entrance into World War II. The cover featured Captain America punching Adolph Hitler. The comic was well received, but Simon and Kirby got a lot of hate mail from anti-war activists.