Like every super-hero, Captain America has a menagerie of colorful villains, but a couple of them are so iconic and bizarre that they stand out above the rest.
First we have.....
The Red Skull!
Nazi tool of terror, the Red Skull first appeared upon the pages of Captain America issue 1 (1940) and has been a villain rarely topped, and to this day is one of Marvel's (Disney's ooh, it hurts to say that) all time greatest trouble-makers. Always a thorn in Cap's side he's been defeated many times but always returns.
The Origin of the Red Skull
Ah, Baron Zemo; creator of Adhesive X, leader of the Masters of Evil and murderer of Bucky Barnes! Forever blaming Captain America for sticking that pink mask to his head and Cap always seeking revenge on Zemo for killing his sidekick these two would go head to head in the early issues of the Avengers. Cap, on a personal vendetta, finally defeated and killed Zemo in Avengers #15, one of the first major character deaths in the Marvel universe (and he actually stayed dead).
The Swordsman first appeared as an enemy of Hawkeye of the Avengers back in 1966 but when the Avengers refused to let him join he took is frustrations out on Captain America. Beefing up his sword with the help of the Mandarin and then joining the Lethal Legion with Power-man and the Enchantress, he was a thorn in the side of the Avengers until his finally joining them years later.
Bartroc aka The Leaper
A crazy frenchman who liked to kick folks in the face (boxing with his feet) was after the Inferno-42 cylinder in Tales of Suspense (1966) when he crossed paths with Captain America. Though an enemy of Cap, he switched sides many times to aid the star-spangled hero as Bartroc determined him to be a 'man of honor'. Oh, and he spoke with an outrageous French accent!
A Jack Kirby creation, this mad Nazi sympathizing scientist had a bunch of weird gizmos to toss at Cap as well as a gun that shot yellow goop and and project his conscience.
Who other than Jack Kirby can create this nightmare! The legendary MODOC (Mental Organism Designed Only for Killing). Working with AIM against S.H.I.E.L.D. he ran across Cap a number of times. Mostly just jealous of Cap's bod, the horrific Kirby creation tried to off our hero a number of times.
One thing I want to point out is that most of these villains were created by Jack Kirby (as was Captain America). It proves, once again, that Kirby was the master creator of the Marvel Universe.
Captain America Week:
Day 1: Eat it Hitler!
Day 2: Captain America Must Die!
Day 3: And A Phoenix Shall Rise
Day 4: Bring On The Bad Guys!
Day 5: Silver Screen Hero