Final answer:
A character that remains the same throughout a story is known as a static character. Static characters contrast with dynamic characters, who do change and develop. Static characters can also be flat, which indicates a lack of depth in characterization.
Step-by-step explanation:
In literature, a character who does not change from the start to the end of the story is called a static character. Unlike dynamic/round characters who experience change and development throughout the story, static characters remain consistent in their personality, outlook, and behavior. It's important not to confuse static characters with flat characters, though they can often coincide. Flat characters are not fully developed, representing one or two traits, and are used primarily to support the story without much depth. Meanwhile, a foil is a character that contrasts with another, usually the protagonist, to highlight certain traits or themes.