Rejected by the army during World War II but still intent on serving his country, Steve Rogers volunteered for a Super Soldier project that would give him increased physical capabilities greater than those of all but the mightiest human athletes. It worked, and once given a uniform and shield, he became a patriotic symbol in his fight against the Axis powers before disappearing mysteriously. Flash forward many decades, and a new generation of superheroes found him frozen in suspended animation. Once thawed he became a member, and later leader, of the Avengers.
Captain Patriotic: Though he's a man of the American Dream, rather than the American government.
Crazy-Prepared: Captain America has spent a lot of time analyzing the data files the Avengers have compiled on all the major supervillains. No matter who he faces, chances are Cap already has a good idea of their strengths and weaknesses.
Dating Catwoman: Diamondback, who reformed in part because of his influence.
Determinator: If anything Cap has can be likened to an actual super power, it's his absolute refusal to give up. Even friggin' Thanos has seen this firsthand◊.
In the regular Marvel verse, Weapon X is really Roman Numerals and is actually Weapon 10, and the Super Solider Serum that made Cap was actually Weapon 1.
Genius Bruiser: Part of what makes Cap so formidable: he backs up his physique and fighting ability with a sharp tactical mind and leadership skills. There's a reason he's been the Avengers' leader since the day he joined.
Luckily My Shield Will Protect Me — Cap's shield is unbreakable and invincible. It also serves for both offense and defense, since Cap can throw it to attack his enemies from long range or beat them with it in close combat. Its unique alloy even makes it able to damage enemies that might otherwise be immune to physical harm-the iron in it is harmful to demons, the vibranium causes pain to energy-based creatures, etc.
Made of Indestructium: His shield is made of vibranium, proto-adamantium and an unknown third component. Not even regular adamantium can cut it.
After its destruction upon hitting the God of Fear, Iron Man has repaired it using mystical Asgardian metal Uru, making it even more durable.
The Spymaster — Served as one in the Nick Fury mold after coming back from his death following Civil War, as "head of National Security". He operated without the shield and his iconic costume, and under his real name, as Bucky was already serving as Cap. It didn't stick.
Super Reflexes: Not only can Cap always position his shield to block attacks, but even when he is chemically mindcontrolled, nothing can prevent him from reflexively moving his shield arm to block attacks with his shield.
Formerly Steve Rogers' Kid Sidekick during World War II, when he was known as 'Bucky'. He was apparently killed shortly before Steve was frozen in suspended animation, but was recently revealed to have been captured, near death, by the Soviets. Equipped with a cybernetic arm and Brainwashed into becoming the assassin known as the Winter Soldier, he played the role of a villain until Steve brought him back to his senses and had him reform. With the apparent death of Steve, Bucky took the mantle of Captain America with the blessing of Tony Stark.
Classical Anti-Hero: Since becoming Cap, his desire to atone for his acts as the Winter Soldier was compounded with serious doubts as to whether or not he actually deserves the mantle and whether or not he can do it justice.
Indy Ploy: In contrast with Steve's Crazy-Prepared-ness, his tactical sensibilities often manifested as this when he became Cap.
Kid Sidekick: Zig-Zagged; he fit the mold in the 40s, but Ed Brubaker's Retcon introduced the idea that this was just a cover story, and that he was really the advance scout and go-to guy for the dirty jobs that Cap couldn't/wouldn't be seen doing.
Red Baron: The Winter Soldier. Even his Soviet superiors called him that, though that's probably because they were privately having a laugh over the fact that they were using Captain America's pal to undermine America and didn't want him to catch on.
The Howling Commando. The SHIELD Ramrod. A 90-year-old soldier/CIA agent/spymaster/fugitive. Considered to be one of the good guys by pretty much every hero on the planet, partly because the idea of not being on his side is kind of terrifying.
Killed Off for Real: Was considered dead in the comics from 1978 to 1995, but came back. Writer Ed Brubaker once commented that he was glad Mark Waid had resurrected Sharon during his run, or else Brubaker would have had to do it himself. Waid stated in interviews at the time of his run he was a bit surprised she hadn't been brought back long before. Her "death" was something Cap only observed on a recording in the original story, which in comics is all but a blazing signal that something fishy is up.
The Reveal: He was initially introduced as an enthusiastic social worker. However, it was later revealed that this was a Cosmic Cube-induced reality warp and he was really a professional criminal, gang member and racketeer before the warp.
Brock Rumlow was a petty thug and hit man, the lowest trash imaginable. Then he was recruited by the Red Skull, and became even worse. A frequent enemy of Captain America, he was the man that shot Steve Rogers at the end of Civil War. A huge fan of the Red Skull, Crossbones is near as bad as his boss, and is utterly devoted to whatever Neo-Nazi cause the Skull and his daughter are embracing this week.
Ascended Fanboy: A particularly ghoulish version of this trope, Crossbones was in fact a huge fan of the Red Skull before his idol offered him a job.
Axe Crazy: Crossbones is a threat to everyone around him, and takes joy in hurting others.
Badass Normal: A good enough fighter to keep up with Captain America, despite his lack of superhuman powers.
Averted for a bit while he was a member of The Thunderbolts, gaining some sort of energy beam power from inhaling corrupted Terrigen Mists. It appears to have been only temporary, however.
From Nobody to Nightmare: Just another angry street kid who ended up enrolling in Taskmaster's school for supervillains. He got a job with the fake Red Skull, who sent him to attack Arnim Zola and the real Red Skull. He impressed the latter, and the rest, as the cliche goes, is history.
Villainous Friendship: Type III with The Red Skull. The Skull might not see Crossbones as anything other than useful muscle, but Crossbones worships the ground The Skull walks on, and has a full blown Freak Out when he dies.
Unholy Matrimony: They aren't married, but Crossbones and Sin have a thing for each other.
AKA: Ophelia Sarkkissian
One of the leading figures in the terrorist organization HYDRA and a notorious international terrorist, Madame Hydra, alias Viper, is an Ax-Crazy psychopath and a nihilistic lunatic who frequently engages in attempted mass murder schemes that have no obvious benefit. She is associated with the Serpent Squad.
Dating Catwoman: She is Wolverines' ex-wife; she blackmailed him into it, and in turn he got the divorce by refusing to give her medical treatment otherwise. Its implied she had started to develop real feelings for him.
Even Evil Has Loved Ones: She may have cared about Wolverine at some point, and she definitely had feelings for the Silver Samurai.
The daughter of the Red Skull and a washerwoman who died in childbirth, Synthia Schmidt was raised by one of his loyal henchmen (Mother Night, The Skull's occasional lover) after he was persuaded not to kill her for being a girl. She is just as demented as her dad, typically running the Serpent Squad on his behalf, and has been romantically involved with Crossbones. As of Ed Brubaker's run she has been disfigured, and taken over her father's role as The Red Skull.
Abusive Dad: As Sin says herself, they only parental thing The Red Skull did for her was give her a name.
Dark Action Girl/Faux Action Girl: Sin's very good at shooting up civilians, police officers, and other red shirts. How well she handles herself when confronted with trained opponents like Captain America, the Winter Soldier, or even Sharon Carter seems to vary from issue to issue.
Younger than They Look: She was aged to adulthood when she was a girl, which also gave her psychic powers. She was aged further to an old woman, then de-aged again to a young adult, losing her powers in the process.
A group of Snake-themed mercenaries led and founded by the first Viper, until he was murdered and replaced by Madame Hydra, who took over the group. Since then the leadership has changed hands from time to time, but she is still associated with the team. The most notable sometime member is Sin.
Amazon Brigade: The Ultimate version, and the mainstream version to a lesser extent.
I Cannot Self-Terminate: At one point, Machinesmith wanted to end his cybernetic existence, but found that he'd installed safeguards against it, so devised an elaborate Suicide by Cop plan to have Captain America do it instead. It didn't stick.
Rogues-Gallery Transplant: As Mister Fear, he was an enemy of Daredevil, but after turning into Machinesmith, he became mostly a Captain America foe.
AKA: Karl Morgenthau
Flag-Smasher explains his politics
The son of a Swiss diplomat who was murdered by xenophobic Latverians. He becomes an anarchist who hates the idea of nations, believing that they cause hatred and violence. He has since died and been succeeded by a second Flag-Smasher, who has clashed with Spider-Man and Nomad among others.
Badass Normal: A capable athlete, and master of shotokan karate-do. Though when compared to some of Cap's other enemies, he seems a bit lacking in this department.
Western Terrorists: Operates as the leader of terrorist group ULTIMATUM, striking out at symbols of nationalism.
Baron Heinrich Zemo
Cap's archenemy from the Silver Age, created in a retcon. Heinrich Zemo was a Nazi scientist who created an adhesive that was nearly impossible to dissolve. In a tussle with Captain America, his purple hood was glued to his face by his invention and he swore vengeance, eventually being the cause of Bucky's "death." Zemo survived the war and became active when he learned that Cap was back, coming into conflict with the Avengers and even forming the first Masters of Evil. Heinrich was eventually killed in battle, with his son Helmut succeeding him as Baron Zemo.
Archenemy: Was Captain America's during the first twenty issues of Avengers, and his actions continue to inform those of Captain America, Bucky, and his son, Helmut, to this day. His team, the Masters of Evil, were, and continue to be, the archenemies of the Avengers.
Badass Bookworm: For a guy who spent most of his life in a laboratory, Zemo's a pretty capable fighter.
Badass Normal: Zemo possessed no superhuman abilities, yet he could not only match Captain America in a fistfight, but led a group that included The Black Knight, The Enchantress, The Executioner, The Melter, and The Radioactive Man.
The Big Bad: Of the original Masters of Evil and any storyline involving them.
Cool Mask: His purple mask is quite cool. Good thing too, seeing as it is glued to his face.
Emperor Scientist: Downplayed. Heinrich was the emperor all right, but of a tiny kingdom deep in the South American jungles.
Evil Genius: To the point where even the Enchantress and the Executioner have to respect his intelligence.
In the Blood: Arrogance and a penchant towards treating others as the lowest forms of life are definitely in the Zemo blood. Heinrich's interest in human experimentation actually began with his father, who conducted similar experiments during WWI.
The son of Heinrich Zemo, Helmut got his start trying to avenge his father's death at the hands of Captain America. He's since gone on to be a fairly major player in the Marvelverse, founding the second Masters of Evil, and the Thunderbolts, and walking the line between Well-Intentioned Extremist and out and out villain.
Aristocrats Are Evil: He's a baron after all, and believes his aristocratic heritage entitles him to rule.
Avenging the Villain: Helmut's original motive was to kill Captain America because he killed his father.
Badass Normal: Has no powers, but regularly fights the likes of Captain America and the Avengers. He usually has a contingency that will allow him to deal with his opponent's plans anyway; it's only when these contingencies fail (as happened during his battle with Moonstone at the end of the initial run on Thunderbolts) that he's in trouble.
The Big Bad: Of his fare share of arcs, particularly those involving the Masters of Evil.
Even Evil Has Standards: Assassinated one of his ancestors during a time-travel jaunt after he found out the man was a rapist and a mass-murderer who did it all For the Evulz. He later clashed with said ancestor's son for similar reasons, and intervened when he thought he found another ancestor harassing a girl (the two were actually in love, and he let them carry on accordingly).
Well-Intentioned Extremist: At this point Helmut's goal is to take over the world to make it a better place. That doesn't mean that he's not an Axe Crazy terrorist who's willing to perform some truly heinous actions for the sake of the "greater good."
An Austrian psychiatrist and hypnotist, Johann Fennhoff is a Neo-Nazi and regular associate of Arnim Zola and The Red Skull, battling Captain America independently, and on their behalf. A poor combatant, he relies on his Compelling Voice to make others do his fighting for him.
Compelling Voice: Can force people to do what he wants with just a vocal command.
Evil Genius: Played this role in Red Skull's organization along with Zola.
Even Evil Has Standards: Like most villains Faustus finds the Red Skull vile. When he realizes the Skull is going to kill him for his failures in one of his plots he helps Sharon Carter escape and comments he would not leave anything he cares about in the Skull's custody regarding the Skull's plans for Sharon's child.
Villainous Rescue: Repeatedly saved Captain America from death. One time in particular Cap was going to be killed by a pack of sharks, Batroc grabbed a knife and dived in because he couldn't stand the thought of "so great a fighter dying so ignominiously." He was able to kill a shark, and its bleeding body distracted the pack long enough to let them both escape.
Strucker: I am the supreme HYDRA, Baron Wolfgang Von Strucker, I witnessed the fall of nations, betrayed beliefs and ties of brotherhood abandoned by modern times. Defeat only serves to light within me the flame of my obsession. My desire is eternal.
Dr. Deidre Wentworth is a superpowered misandrist that originally opposed Captain America with the Femizons, and later went on to join Norman Osborn's second iteration of the Dark Avengers as Ms. Marvel. She is currently the Minister of Education for the Advanced Idea Mechanics.