Disney+'s exciting first trailer for the series, the U.S. Agent will play a key role. This dark reflection of Captain America has been a big part of the Marvel comics since back in the '80s.
For a time, the U.S. Agent was Captain America in the comics. It's possible that the series could be about John Walker assuming the role, even though Steve Rogers left the shield to Sam Wilson. Walker's comic book history could feature clues to what may happen.
The Super-Patriot
John Walker has been a thorn in Captain America's side from the start. He began as a villain, the Super-Patriot, debuting in Captain America #323 in November 1986. He was co-created by writer Mark Gruenwald and artist Paul Neary.
Walker was envisioned as a dark inversion of Captain America, someone who was a patriot but embraced a more rigid form of nationalism than Steve Rogers ever did. Though well-intentioned, Walker was far more violent and merciless than Captain America.
The New Captain America
Within just a few issues of his first appearance, John Walker vaulted into the actual role of Captain America. Steve Rogers resigned from the position after being asked to report to a government entity, the Commission On Superhero Activities. Walker is selected by the committee to take over, though he's initially reticent.
The move was very similar to the Knightfall storyline from the 1990s, in which Bruce Wayne steps down as Batman (though involuntarily in his case, thanks to the first version of Bane) and is replaced by a more radical, younger man.
Grim N' Gritty
Batman, Superman, and Green Lantern would all be replaced by new versions in the '90s, but Marvel actually pioneered this in the '80s. Numerous characters went 'dark,' including Spider-Man with his famous black costume that eventually spawned anti-hero Venom (and the so-so Sam Raimi Spider-Man 3), Daredevil, and Iron Man.
The so-called 'grim and gritty' era of comics is exemplified by violence and 'darker' characters were borne out of the success of Watchmen and The Dark Knight Returns.
Becoming The U.S. Agent
The effort to boost sales on the title definitely worked, and so did the effort on the part of the creative team to remind people of what Captain America stood for by creating such a stark contrast. Steve Rogers returned to the role of Captain America and Walker was out. He would become the U.S. Agent.
John Walker decided to continue fighting crime, as his own man. He donned a variation of the black costume Steve Rogers wore while away from the role of Captain America. Walker took on the title of U.S. Agent. Though he was fighting for good, he would continue to butt heads with Rogers.
Powers
Some comic book fans might think the MCU has wasted some of its villains and waited too long to introduce U.S. Agent. But he could be appearing at the right time. Without Steve Rogers' superhuman strength, Walker's own superhuman power and durability are bound to cause serious problems for Falcon and the Winter Soldier.
Walker developed his powers as a result of mutagenic experiments by The Power Broker, and combined with his expert martial abilities, is a serious opponent for anyone.
The Buckies
One of the strangest aspects of U.S. Agent's comic book history are The Buckies. Walker initially is an enemy of the nationalistic villains Left-Winger and Right-Winger, or so it seems. He actually has hired them to stage fights to prove his power.
After he becomes Captain America, they become 'The Buckies,' taking their name after Steve Rogers' original sidekick, Bucky Barnes. It's not clear if they'll be in the series yet, but if so, they would definitely be contenders for the best MCU sidekicks.
Tragedy
John Walker went looking for a lot of trouble and it often came looking for him too. His parents are killed by the violent extremist group The Watchdogs and he misses their funeral because of his responsibility as Captain America. This and other events drive him toward mental and emotional exhaustion.
He eventually goes over the edge, but Steve Rogers comes to his aid. Rogers returns to the role as Captain America, and Walker's misery continues. His assassination faked in public and he goes into hiding, given a new cover identity, and hypnotized into thinking his parents are still alive.
West Coast Avengers
The West Coast Avengers are the first true Avengers spinoff team and one of the strongest Avengers teams ever. U.S. Agent, now working covertly for the same commission that put him in the role of Captain America, is assigned as a spy more or less of the west coast team and of The Vision in particular.
U.S. Agent butted heads with pretty much everybody on the team and got into such a huge fight with team leader Hawkeye that both ended up booted from the team.
The Scourge Of The Underworld
A big part of the U.S. Agent's initial adventures culminated in investigating The Scourge Of The Underworld. This costumed vigilante killed criminal superhumans, and John Walker tried to stop him.
He eventually discovered that the Scourge wasn't an individual, but a number of different people who operate in the role. Walker then discovers that his older brother is one of the people involved in the scheme. The Scourge could be a good potential story for the MCU given the characters it's developing.
Force Works
The U.S. Agent remained connected to the larger Avengers family, even as it evolved dramatically in the 1990s. The West Coast Avengers broke up in the early '90s but then reformed as Force Works. This team was ostensibly more focused on natural disasters than battling supervillains.
Walker didn't want to at first given his experience with the former team, but Scarlet Witch convinced him to participate, which could have interesting impacts on the future of the MCU.