Final answer:
A flat character is a simple, one-dimensional character showing no depth or development throughout the story, often summarized by a single sentence or characteristic.
Step-by-step explanation:
The name of a simple, one-dimensional, unchanging character who shows no depth is a flat character. E.M. Forster, in his work Aspects of the Novel, coined the terms flat and round characters to distinguish between those with little depth and those with nuanced, complex personalities. Flat characters can often be summarized in a single sentence and lack the depth and development that round characters possess. They are contrasted with static/flat characters who do not change throughout the story, and dynamic/round characters who do change and develop. Flat characters are sometimes similar to stock characters, representing stereotypical figures with predictable behavior, such as the foolish sidekick or the stern matriarch.
Forster provides an illustrative example of a flat character with Mrs. Micawber from Dickens' David Copperfield, who is characterized by her unwavering declaration, "I will never desert Mr. Micawber". As Forster notes, she remains consistent to this sentiment, thereby encapsulating the essence of a flat character. Conversely, round characters exhibit a depth that allows them to surprise readers in plausible ways, reflecting the unpredictable nature of real-life personalities.