I think that, having now covered the Red Skull and Winter Soldier, the next Captain America film should cover a relatively obscure yet entirely meaningful villain: William Burnside, AKA Steve Rogers II AKA The Grand Director AKA The Captain America of the 1950’s.
The foundation has already been laid with Bruce Banner’s work in recreating Erskine’s formula– it simply needn’t have been the first attempt (and Coulson’s dialog in Avengers indicates it was simply the last in a LONG series of experiments to that end).
Here’s how I figure the backstory works:
In the 1950’s, during the rise of the Second Red Scare, the United States decides it needs a new Captain America to give the masses a symbol to look to, an icon.
They enlist William Burnside, a scholar and College Chemistry professor who has studied Erskine’s work in creating Captain America, to work with Howard Stark in recreating the formula. Burnside proposes using the unfinished formula that created Red Skull (which was retrieved by the Original Cap’s team during their assault on Red Skull’s HQ) as a springboard so they don’t have to redo the whole formula from scratch. Assisting Burnside and Stark is Jack Monroe, a student of Burnside’s who is equally vested in seeing the “rebirth” of Captain America.
After much work (montage time), they create a prototype formula, and Burnside takes two samples for testing.
Before he gets a chance to test it, however, he and Jack witness Hydra agents attempt to do… something despicable. Something COMMUNIST NEO NAZIS would do. Jack and Will inject themselves with the prototype formula, and gain the extra oomf they need to thwart the plot. Burnside and Monroe are legally declared Captain America and Bucky, but soon develop psychotic paranoia that leads them to be subdued, captured, and frozen by agents of an early incarnation of SHIELD.
This can all be explained via a series of flashbacks and a mission briefing from Nick Fury (when the time is right and Steve’s about to quit over a lack of intel, of course).
In the present day, a villain calling himself “The Grand Director” is leading an anti-American terrorist cell that is managing to outclass the federal agents deployed to stop them. Captain America, Sam Wilson, Hawkeye, and Black Widow are recalled by the government to neutralize the threat. During their battles with Grand Director’s thugs, Hawkeye notes they fight similar to SHIELD troops, and this drives the group to seek answers from Fury, who of course, is not obliging.
Eventually, their backs against the wall, Steve presses Fury for answers as to the Grand Director’s true identity.
Fury looks at him and says “He’s YOU.” and proceeds to relate the story of William Burnside, and mentions that the bodies of William Burnside and Jack Monroe had been stolen following the events of Winter Soldier, possibly by HYDRA agents.
Steve has a “holy shit” moment as he realizes that Grand Director is basically him, just more insane, and probably manipulated by HYDRA. He engages the Grand Director in direct battle, and with some intervention from one of Steve’s allies, Grand Director decides he’d die “before submitting to what America has become” and sets himself on fire.
Steve hits the bar, and muses on the Grand Director’s words, which after “Winter Soldier” hit him harder than they otherwise might have. After some deep reflection, a man delivers a message to Steve: Burnside is alive, and is going to destroy the Hoover Dam as a symbolic attack on the “corrupting transformation America has undergone.”
As Steve arrives at the Hoover Dam with Sam Wilson, Burnside (now in his old Captain America uniform from the 1950’s) explains his motives, claiming that the present-day United States had turned away from its core ideals and more honest basis as he remembered them. He says he “went home for a while, and looked out at the brave new world”, reflected on the current political and economic distress of the United States, and decided that the current government had abandoned its duties and had failed its citizens. Burnside then claims that it would be best to overthrow the government and restart America with a new one that would reflect his view of what America ought to be, his vision as outlined in dialog warped and twisted by an obvious HYDRA influence, while he rants that it is “Captain America’s duty to remove the filth from the American national soul”.
Steve tries to get his would-have-been successor to see reason, but Burnside instead flies into a paranoid rage like the ones that caused him to be arrested in the first place, and Rogers is forced to kill him with his old World War II revolver while Sam manages to thwart the destruction of Hoover Dam, apprehending a slightly more lucid Jack Monroe in the process.
The movie winds down, with Steve talking with Sam Wilson and Black Widow, and while they reassure him that Burnside was insane and further manipulated by HYDRA, Steve merely points out that “While he was crazy and manipulated, he also had a point”, noting that while his ultimate vision for America was just as diseased as the one he saw already in place, “after everything we’ve seen, can we really say we haven’t fought the same demons he did?”
Quiet drama scene finishes, end credits roll, Marvel sets up for the next movie post-credits.
Marvel, get thee to work!