What is a character with very few sides to their personality called?

A character with very few sides to their personality is referred to as a flat character. Flat characters are often characterized by their lack of depth and complexity. They typically embody a single trait or idea and do not undergo significant development throughout the story. This straightforward nature makes them easier for readers to understand but can also lead to a less engaging portrayal compared to more complex characters.

In literature, flat characters frequently serve specific functions within the plot, such as representing a particular stereotype or providing comic relief. Their simplicity allows them to maintain a consistent role, without the internal conflicts and growth that round characters often experience. Round characters, on the other hand, are multifaceted and undergo development, making them more relatable and dynamic within the narrative.