One of the more bizarre rumors earlier this year came during the press rounds for "Captain America: The Winter Soldier". A throwaway comment from screenwriters Christopher Markus and Stephen McFeely led to stories being published assuming that the villain for the third film will be an evil version of Captain America.
In the comics, there was a story arc in which a different man is injected with the super serum to take over the Captain's responsibilities after he's lost in the Arctic. The treatment has psychotic side effects, so he's eventually placed in suspended animation and later revived in an attempt to kill The Falcon.
Earlier today, Markus and McFeely finally put the speculation to rest, telling CBM that the third "Captain America" film has no plans to go all "Superman III" on us:
Markus: That was a smart remark, off the cuff. What I love about that whole run, the whole existence of that, is the sort of single minded desire to retcon everything into continuity, you know? 'But there was five issues in 1950 where he was a jerk!' I know he was a crazed college professor who had plastic surgery, but I think we can honestly say that he will not be making an appearance.
McFeely: You know, there's probably 20 minutes of movie there. There's something interesting about a guy who so desperately want to be [Captain America] and be a tribute...I just don't think it's a whole movie.