This is the main character in your story – it’s who the story is centered around. He/she doesn’t have to be good, nor do we necessarily have to root for him/her. The protagonist is the character who’s objective is the main focus which drives our story forward.
In more elevated story telling, the protagonist is referred to as the character who experiences the most personal change within our story. Some examples:
Oscar Schindler (SCHINDLER’S LIST) – a loyal Nazi changes from a money-hungry business man to a passionate humanitarian who’s mission is to employ Jews and save them from execution.
Michael Corleone (THE GODFATHER) – a patriotic standing military man comes home from the war and becomes the head of a large criminal organization. Again, our protagonist doesn’t have to be a good person.
Red (SHAWSHANK REDEMPTION) – People will argue that Andy Dufresne is the protagonist in this film, however, Red is the character who experiences the most personal change in the film. He starts off as a lowly man who’s lost all hope, to a liberate free spirit who found happiness for the first time in decades. Therefore, one could argue that Morgan Freeman’s character is the protagonist.