Baron Zemo: Heinrich Zemo was one of the elite Nazi scientists during World War II. After his death, his son Helmut Zemo took on the role and continued a heated rivalry with Captain America; he has teetered between heroics and villainy due to his association with the Thunderbolts, an ultimately-reformed version of the Masters of Evil that took on false hero guises in the 1990s absence of the Fantastic Four, Avengers and other high-profile heroes.
Batroc the Leaper: A French mercenary and leader of his own brigade of criminals, Batroc's Brigade.
The Corporation: A business-like criminal organization, which employed numerous super-villains against heroes across the nation. Captain America did battle with many of their surrogates, including Blue Streak, Night Flyer, Ameridroid and Vamp/Animus.
Karl Stryker: A Nazi sympathizer who used a hydraulics-powered combat suit to combat Captain America. His son Viktor took revenge on Captain American soon after, but was killed in the process.
King Cobra: Costumed super-villain, known for a phenomenal (mutated) mastery of his musculature in combat situations, and member of the original Serpent Squad. Also worked commonly alongside Mister Hyde against Captain America and other heroes.
Kligger: Former leader of The Corporation, the criminal guise of Senator Eugene Stivak. Often accompanied by his aide Veda (who he personally killed when she eventually gave up her allegiance to the organization)
Machinesmith: A master robot-maker (once a villain known as Starr Saxon) who became a living, cybernetic-system program (artificial consciousness), equipped to transmit itself into virtually any electronics system at will.
Madame Hydra: Leader of HYDRA. She is also known as the second Viper.
Master Man: A Nazi super-soldier who, like Steve Rogers, was enhanced by a Nazi-version of the American super-soldier serum.
Minister Blood: Hypnotist agent of the Red Skull. Brother of Mother Night.
Mister Hyde: Chemically enhanced super-villain. Worked commonly alongside King Cobra against superheroes, especially Captain America.
MODAM (Mental Organism Designed for Aggressive Maneuvers): An A.I.M. agent who, like MODOK, was originally a tech agent for the organization mutated for various offensive measures against their enemies.
MODOK (Mental Organism Designed Only for Killing): A former A.I.M. tech transformed with advanced mutagenics into the organization's leader. Later disassociated itself from A.I.M. and works alongside other "genius-level" villains in the Marvel Universe.
Mother Night: Ally of the Red Skull and Crossbones, former leader of the Sisters of Sin and former member of the Skeleton Crew. Sister of Minister Blood.
Super Patriot: John Walker was Captain America's replacement during the 1980s (when his removal from the heroic role was orchestrated by The Red Skull). He was an unwitting rival to Steve Rogers but nonetheless a hero in his own right, and ultimately he became an ally to Captain America as the renamed U.S. Agent.
Swine: Hector Santiago, the dictator of Rio De Muerte ("River of Death"), slavemaster and leader of a small private army.
Winter Soldier: Codename used for Cap's former WWII partner Bucky Barnes, who, though thought dead, was a notorious, mysterious Soviet assassin for decades. Ultimately overcame his Soviet reprogramming to become Cap's ally (and for a time the new Captain America) once again.