The protagonist is the main character of a story, and the main playable character in the Manhunt games. Traditionally, a protagonist is the main figure of a piece of literature or drama and has the main part or role. Alternatively, the phrase denotes a primary advocate of or proponent for a cause or movement. The main character can be a hero or a villain in a story - it is just the character with the lead role. In literature, the protagonist is characterized by his/her ability to change or evolve.
It should be pointed out that the protagonist is not always the hero of the story. They may kill other characters for survival or revenge but he/she is still considered the lead character.
All protagonists of the Manhunt series share some similar qualities. All protagonists escaped or rescued by some in a locked and isolated place (Danny and Cash, respectively) or controls the main character (like Leo). Protagonists are always start at a place where they woke up then eventually betrayed by the antagonist.
The opposite of a protagonist is an antagonist, which is the main person working against the protagonist and his actions. Again, this can be a villain or a hero, though usually a villain.
Most antagonists in the game always show up as a voice, guiding the protagonist in their impending doom. But they are always get killed by the protagonist.