The Princess Diaries, a young adult novel and the first in the series of the same name, follows the story of ninth-grader Mia Thermopolis, who discovers that her estranged father is actually a prince, making her a princess. Mia, with her gangly limbs and busy hair, begins taking etiquette lessons with her grandmother in order to learn how to act like royalty. At the same time, Mia must deal with other issues, like fighting with her best friend Lilly and her mother dating one of her teachers.
Mia Thermopolis : Describes herself as a five-foot nine, flat chested, freshman, freak; also known as Amelia Mignonette Grimaldi Thermopolis Renaldo, Princess of Genovia. Mia loves to write, has a tendency to obsess over everything that happens to her, is a vegetarian, identifies as a feminist and is currently failing algebra and many other subjects.
Grandmere : Mia's grandmother, who loves Sidecars, is highly critical of everyone around her. She has a hairless poodle, Rommel, and she calls Michael Moscovitz that boy . Her full name is The Dowager Princess Clarisse Renaldo. Mia and her Grandmother don't get along with each other for most of the story.
Lilly Moscovitz : Mia's bossy activist best friend, who has her own television cable show, Lilly Tells It Like It Is.
Michael Moscovitz : Lilly's older brother, who is extremely smart and according to Mia, is attractive. Also Mia's crush.
Lana Weinberger : Head cheerleader, initially Josh's girlfriend, and the person Mia dislikes most at her school.
Josh Richter : Mia's crush, "six feet of unadulterated hotness." Originally dating Lana at the beginning of the story, he is shown to have manipulative tendencies.
Helen Thermopolis : Mia's quirky painter mother, who surprises Mia by dating her algebra teacher. She is described as irresponsible.
Philippe Renaldo : Mia's royal father, who is the prince of Genovia. He had Mia out of wedlock, and is constantly annoyed by his domineering mother, has many girlfriends, and tells Mia that she is a princess after he is no longer able to have children because he had cancer.
Tina Hakim-Baba : A girl whom Mia befriends throughout the novel. Her father is an oil man sheikh who is worried that she will get kidnapped. She originally is shunned because her overprotective father forces her to have a bodyguard (Wahim), but she and Mia quickly become close.
Lars : Mia's bodyguard. He follows her almost everywhere and lives in the Plaza. Has some serious blackmail on Mia, having followed her around everywhere.
Fat Louie : Mia's very fat cat who is attracted to anything shiny.