Warning: Spoilers for Captain America: The Winter Soldier

Captain America: The Winter Soldier hits home video on September 9th and we had the opportunity to speak with co-directors Anthony and Joe Russo on this week's episode of the Screen Rant Underground podcast. In addition to chatting about release dates for the film and its upcoming three-quel, box office expectations and Hawkeye's (Jeremy Renner) original role in it, we also got more background on some of the things said in the commentary featured on the film's Blu-Ray special feature section.

One of the major highlights of Captain America 2 and what made it stand out compared to its predecessor and the rest of the Marvel Cinematic Universe is its use of villains. Not only are the primary antagonists better-developed than in other Marvel films, with more clear motivations, but they bring a real sense of danger to the screen for our favorite heroes.

With Sebastian Stan's Bucky Barnes returning as the deadly Winter Soldier and used as a super assassin by Alexander Pierce (Robert Redford), Captain America: The Winter Soldier arguably has the best villains, so given what happens to the pair by the end of the film, how does the followup, Captain America 3, build off that and top those those characters?

Anthony Russo: Here’s the thing. The thing we love about Bucky is he’s a really complicated character; very tragic, complicated character. Here’s a guy, when you look at him, is he the world’s worst assassin or is he the longest serving POW in history? You could look at him as one of two things. Either he’s innocent by reason insanity or the equivalent of that, in terms of not being responsible for his actions because he was brain controlled, or he’s a monster. It’s a very complicated place. It’s a hard place to move forward from that. In relationship to Cap, it’s like is Cap ever going to be able to access the guy he used to be?

Sebastian Stan as The Winter Soldier in 'Captain America 2'

Joe Russo: And if he can’t, well who is Winter Soldier? Is he Bucky Barnes anymore or is he somebody knew? So those are all really interesting questions to ask with him. It’s our job on the next one to outdo the villain from the last one. But because that’s a mandate of ours, it’s always something we put an incredible amount of focus on. The stakes aren't high enough. The audience doesn't feel those stakes. If the characters aren't in jeopardy continually throughout the film, then you lose a certain narrative momentum to the movie. As we said, you can only define the hero against the villain. So the greater the villain, the greater definition you get out of your hero.

Long before The Winter Soldier hit theaters, Robert Redford had semi-spoiled the fact that his character would be the villain of the movie and that led to speculation and other rumors that he could be a modern version of The Red Skull - a character who hasn't been seen since teleporting away in Captain America: The First Avenger and who we know was part of early drafts of The Avengers script. Could The Red Skull then return to the MCU in future Captain America stories or other Marvel projects?

Anthony: We can’t really comment specifically in terms of where we’re going with it, just because we don’t want to spoil anything for anybody. But certainly, look. That’s the great thing about the Marvel universe, is anything is possible. All these characters exist. And as we've seen on the publishing side, there’s very inventive, creative ways to make characters relevant again and surprising ways to make the characters relevant again. He’s a great character. Whether or not he finds his way back I can’t really say.

Marvel Comics Civil War Crossover

We don't know much about Captain America 3, not even an official title, so it's hard to figure out who the villains will be, let alone the heroes who could be in it. Stay tuned for more from our interview with the Russo brothers!

The real question is - will we get MODOK?! That's a character writers Christopher Markus and Stephen McFeely have long been interested in. Here's a list of other villains from Marvel Comics we'd like to see in Captain America 3.

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More: Captain America 3 Begins Shooting in April in Atlanta

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Captain America: The Winter Soldier is produced by Kevin Feige, directed by Anthony and Joe Russo, from a screenplay by Christopher Markus & Stephen McFeely, and stars Chris Evans, Scarlett Johansson, Sebastian Stan, Anthony Mackie, Cobie Smulders, Frank Grillo, Emily VanCamp and Hayley Atwell, with Robert Redford as Alexander Pierce and Samuel L. Jackson as Nick Fury.

Captain America: The Winter Soldier releases on Disney Movies Anywhere August 19, 2014, and on 3D Combo Pack, Blu-ray, DVD and On-Demand September 9, 2014. Captain America 3 opens in theaters May 6, 2016.

Follow Rob on Twitter @rob_keyes for your Marvel movie and TV news!