In terms of practicalities, Cap's biggest problem lies in his origin story: scrawny Steve Rogers volunteers to test the super soldier serum, thereby becoming the red, white and blue hero he's known for today. Outside of Christian Bale, I can't think of many actors that could leap from a rail thin frame to the muscular build required of Captain America -- so instead, I'll focus on the post-serum Cap. With that stipulation, here are five actors with what it takes to bring Marvel's most patriotic superhero to the big screen.
JOHN BARROWMAN: The "Torchwood" star already has a Captain to his name, so what harm could come of one more? As the mostly heroic Captain Jack Harkness, John Barrowman has demonstrated all of the charm and poise you'd expect from a superheroic Steve Rogers -- but more importantly, he already wants the role.
"You know what I want to play? Captain America," Barrowman told a crowd gathered at Comic-Con, though he added that it "so won't happen." I definitely think it could, especially when you consider he already has the geek cred from "Torchwood" and "Doctor Who."
AARON ECKHART: With his involvement in the "Batman" universe effectively finished, Aaron Eckhart is without a comic book franchise to call his own. But take one good look at his blonde hair, the chiseled chin and his overall physique -- on appearance alone, it's clear that this guy could pull off Steve Rogers.
A real testing ground will be "Battle: Los Angeles," the science fiction action film starring Eckhart. In the film, the "Dark Knight" alum will play a hardened military leader, which should provide all the evidence we'll need to see if he's the right man for Captain America's job.
NATHAN FILLION: Between his history with Joss Whedon and his fan casting as Hal Jordan, Nathan Fillion is clearly a favorite in the comic book community. With Green Lantern spoken for, Fillion supporters need to turn towards a different superhero vehicle for the actor... and Captain America could be the ticket.
While he lacks the physical build of some of these other competitors, Fillion more than makes up for it with a natural aura of heroism, wittiness and charisma. If he dyes his hair and hits the gym just a little bit harder, he could easily pull off the role of Steve Rogers. And sure, he's not an American actor, but this is America we're talking about -- it's the land of opportunity, folks. Let's give Fillion a shot!
ALEXANDER SKARSGARD: If we're already forgiving the Canadian-born Fillion, then we have to at least ponder the possibility of Alexander Skarsgård. The Swedish actor has achieved a cult following for his role as Eric Northman on "True Blood," but it's his performance as an American soldier in "Generation Kill" that solidifies his ability to play Steve Rogers.
Furthermore, the actor is already on Marvel's radar due to his near miss with "Thor." Maybe the Marvel Studios bigwigs thought him better suited for a shield than a hammer. Judging by his physique, his fan base, his acting ability and his past experience with Marvel, I think Skarsgård has a better chance of becoming Captain America than some might give him credit for.
MARK VALLEY: Much like Eckhart, "Fringe" actor Mark Valley is a dead ringer for the chiseled Steve Rogers. He also has a strong push from fans, previously winning over Newsarama readers in their 2008 Captain America casting call.
Valley also has the advantage of getting previous comic book experience in the form of "Human Target," the upcoming television adaptation of the DC Comics series. Once Valley familiarizes himself with viewers in that capacity, it might not be long before Marvel starts knocking on his door with a star-spangled suit in hand.
Let the debate continue -- who do you think should play Captain America? Let us know in the comments or on Twitter, and let us know some other characters you'd like to see in a future installment of SECRET IDENTITY!