Marvel has confirmed that Spanish-German actor Daniel Bruhl (Rush, Inglourious Basterds) has joined the cast of Captain America: The Winter Soldier. His co-stars being Chris Evans, Robert Downey Jr, Chadwick Boseman (as Black Panther), Sebastian Stan, and possibly Jeremy Renner. Production is about to begin soon with the Russo Brothers back as the directors, I'm sure more casting news will spring-up soon. However, Marvel isn't revealing who Daniel will be playing in the film, making the role a bit mysterious.
Variety is reporting that Daniel will be playing one of the villains in the film, not the main one. We have kind of figured that Tony Stark would be a theological villain of the film. They add he might be the main baddie of Doctor Strange. Which sounds weird to me, since Strange and Cap don't really share villains.
It might be a safe to assume that Brhul has taken the role of Baron Zemo, or a modern take of the current head of the Zemo family. Who has been active for generations, including during World War I and World War II. During the second World War, becoming a rival of the Red Skull and a collaborator with the Nazis. The character was even teased in a piece of museum concept art from Winter Soldier, a snow-covered battle scene named OPERATION: ZEMO. He's one of the only WWII era villains still unused, and is actually even more well-known than HYDRA's Baron Strucker from Age of Ultron.
The legacy villain has been a fan-favorite and finding a place for him in the film universe has been a bit tricky. I really do hope they use Zemo instead of resurrecting Red Skull, since this could be our last romp with Rogers as Captain America. Flashbacks would be nice, but since Zemo is replaced by the next generation he could be around in present time too.
The connection to Strange might suggest the role might be Baron Mordo. This doesn't make too much sense, since we likely won't be getting an appearance of Strange or his antagonists in Civil War. Then again, Black Panther villain Klaw might be in Age of Ultron and Panther being in Civil War. They could try to setup Stephen Strange in a similar way, since the two productions are filming in the same year. However, Mordor doesn't really have connections to the Civil War story as much as Zemo. There is some speculation that the two characters could be combined, but that sounds like a waste to me. It should be noted that Doctor Strange frontrunner Benedict Cumberbatch co-starred with Brhul in the Fifth Estate. Re-teaming the pair wouldn't be hard to imagine.
The only thing I don't like about Baron Mordo, is his name. We already have a Baron villain with Baron Strucker and his last name is eerily similar to Middle Earth's Mordor. I wouldn't put it past Marvel to try to combine Zemo and Mordo into one character.
I also wouldn't rule-out the more obscure John Flasworth aka Baron Blood. A Nazi vampire who just happens to be a that could fit into both Strange's occult universe and Cap world of Marvel being setup in Doctor Strange. Since he's a vampire he would be ageless, I'm not sure that's the type of villain that would be suited for Civil War.