There are several terms that could be used for a supporting character. It all depends on the function that the supporting character fills.
I'll start a list and hope that others contribute:
what part of the story where things turn around for the main character is called the
The character who is telling the story is called the narrator. The narrator sometimes plays an important role in the story and can be the protagonist, or it can be someone on the sidelines who does not take part in the main action.
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The main character is the protagonist, and his/her enemy is the antagonist.
Oh, dude, the fourth character is actually just called the "quaternary character" or "supporting character." I mean, unless you're writing a story about dragons, then maybe they could be the Quadragonist, but that's a whole different genre, man. So, like, stick with "quaternary" if you want to sound all fancy and stuff.
The beings in a story are called characters
The character is called a supporting character
If a character is not a main character, they would be a supporting character.
The second main character in a book is usually referred to as the "deuteragonist." This character often plays a significant role in the story and interacts closely with the main protagonist, helping to drive the narrative forward.
A supporting character in a book is a character who plays a secondary role to the main character or protagonist. They often provide assistance, guidance, or conflict to help develop the main character's journey and story arc. Supporting characters help to enrich the narrative and add depth to the overall storyline.
A person in a story is called a character.
A major character is the focus of the story. Major characters are different at the end of the story than they were at the beginning of a story. The same is not so true of supporting characters.
The main female character of a story is usually called the main character. In Epics the main female character is called a heroine.
Dynamic Character
The supporting character. This character had a minor role in the story, such as the protagonist's (main character's) best friend, or sister, or whatever, but not very many details are usually given about him/her. The author doesn't usually go in depth about supporting characters.
Character development or character arc.
Do you have a pic or what the story is called?