The Shadow Protagonist
In the pantheon of archetypal figures who appear and re-appear regularly in fiction of all kinds, there is another kind of antagonist. This is the character construct who bears a close resemblance to the protagonist himself or herself. This character is usually working for the main antagonist, or shares the goals of that figure, so he or she is both an enemy to the protagonist and yet very much like the protagonist in many ways.
This is the Shadow Protagonist.
• In The Lord of the Rings, this is Gollum, the ancient hobbit twisted by the One Ring.
• In the larger Star Wars series, Darth Vader is the Shadow Protagonist while the Emperor is the main antagonist.
• In the Harry Potter series, Malfoy is the Shadow Protagonist to Harry.
In Captain America: The Winter Soldier, Steve Rogers’ Shadow Protagonist is clearly the Winter Soldier himself, his former partner transformed into a brainwashed assassin.