The answer is indeed: character.
We may define character as a person represented in a story, be it a movie or a play, for instance. The queen, her court, her servants, and her villagers would all be characters.
The plot is the story itself, the sequence of linked events that take place in the characters' lives, always in a cause-and-consequence manner.
Diction is the style in which the authors choose to write, the word choices they make. It may also be related to tone and articulation, when it comes to speaking.