A flat character is simple. They are defined by a single trait or idea. They do not change. They do not have complex motivations. They serve a purpose in the story: to support the protagonist, provide comic relief, or represent a type. They are not the focus. They are the background.

The term comes from E.M. Forster's Aspects of the Novel. He distinguished flat characters from round characters. Round characters are complex and change. Flat characters are simple and static. A flat character can be memorable. Mrs. Micawber in David Copperfield is flat but vivid. She always says she will never desert Mr. Micawber. That is her single trait. It is enough.

Flat character characteristics

• Defined by one or two traits.
• Does not change.
• Predictable behavior.
• Serves a specific function.
• Often minor characters.

Flat characters are not bad writing. They are efficient. A story needs them. The waiter who appears for one scene does not need a backstory. The villain's henchman does not need a redemption arc. Flat characters keep the story focused. They do not distract. They support the theme. But a story with only flat characters is shallow. The protagonist must be round. The antagonist should be round. The supporting cast can be flat. The balance depends on the story. A comedy might use more flat characters for laughs. A tragedy needs round characters for emotional depth. The flat character is a tool. Used well, they are invisible. Used poorly, they are stereotypes. The difference is whether they feel like a person or a type. A flat character who is a type is fine. A flat character who is a stereotype is not. The line is thin but important.