Notes on Protagonist and Antagonist!

Protagonist drives the plot forward. 
Antagonist tries to stop him.

The protagonist is the main character, usually the "good" guy in the story. The story mainly focuses on this character's experiences. 

The Antagonist is usually portrayed as the "bad" guy, or the person that goes against the protagonist and way he's trying to do. 

In the Story Mind, the Protagonist is the Prime Mover of the effort to achieve the Story's Goal. The Antagonist is the Chief Obstacle to that effort. In a sense, Protagonist is the irresistible force and Antagonist is the immovable object.

Without a Protagonist, your story would have no directed drive. It would likely meander through a series of events without any sense of compelling inevitability. When the climax arrives, the protagonist would likely be weak. This is not to say that the protagonist won't be convinced to stop trying, eventually, he or she will ignite again and once more resume the drive toward the goal. 

In choosing which of your characters to assign the role of the Protagonist, it doesn't have to be the most powerful character, rather it will simply be the character who keeps pressing forward, even if in a gentle manner until all the obstacles to success are either overcome or slowly eroded.