The two most important characters in your book are your protagonist and your antagonist because they’re the characters in conflict.
“Agon” in classical Greek means “struggle.”
A Prot-agon-ist is somebody who is first in the struggle, who owns the conflict and pushes it forward, defining it by pursuing a goal.
An Ant-agon-ist is somebody who blocks the protagonist’s pursuit of his or her goal, and in doing so, shapes the story. Without an antagonist, the protagonist goes straight for the goal, a boring narrative path. Blocked by an antagonist at various points in the narrative, the protagonist must shift her or his plans, moving in new directions that change the shape of the story.
The important thing about these definitions is that neither one has a moral dimension to it. The Protagonist and the Antagonist are not the Hero and the Villain. They are two characters who block each other in the pursuit of goals that are vital to them. The antagonist’s goal should never be just to stop the protagonist; he should be a complete character in his own right with his own goal, the protagonist of his own story.
Cinderella wants to go to the ball to meet the prince and marry him, so she makes a beautiful dress. When her stepmother sees the dress, she tears it up and locks the girl in her room. It’s a story about a young girl whose plans to achieve her dream are blocked by a jealous stepmother.
Margaret wants her daughter married to the prince, but her beautiful stepdaughter often outshines the daughter. When Margaret finds out that the stepdaughter has made a dress that will hurt her daughter’s chances, she rips up the dress, and locks her stepdaughter in her room. It’s a story about a mother trying to protect her child from a dangerous rival.
If you change the protagonist, the meaning of the story changes because the protagonist owns the story.
Cinderella wants to go to the ball to meet the prince and marry him, so she makes a beautiful dress. When her stepmother sees the dress, she tears it up and locks the girl in her room. It’s a story about a young girl whose plans to achieve her dream must change when she’s prevented from going to a ball.
Cinderella wants to go to the ball to meet the prince and marry him, but the prince wants to marry a rich, cultured woman. When Cinderella gets to the ball, the prince makes fun of her handmade dress and her provincial accent. It’s a story about a young girl whose plans must change when she is blocked by an arrogant man.
If you change the antagonist, the path of the plot changes because the antagonist shapes the story.