- “Me? A...a princess? Shut up!”
- ―Mia Thermopolis
Mia Thermopolis is the main protagonist of Disney's 2001 feature film, The Princess Diaries, and its 2004 sequel. She is the Crown Princess and later Queen of Genovia. Originally, Mia was once a normal girl, wanting to live a content life and get through high school, until in the weeks leading up to her sixteenth birthday, she discovers the truth of her royal heritage and must decide if she has what it takes to become a true princess.
Five years later, Mia is preparing to assume the throne and officially become Queen but finds her title threatened and is thrust into an arranged marriage, otherwise, she will lose the crown. Mia is prepared to sacrifice her happiness in order to secure Genovia's future, but despite her engagement, she finds herself falling in love with her rival, Nicholas Devereaux.
Mia was born in San Fransisco and raised by her single mother, Helen Thermopolis. Mia never met or knew her father as her parents divorced early in her life, only knowing him through stories and photographs and aware that apparently one of the reasons behind their decision was due to her grandmother's disapproval of their relationship. Despite her father not being present in her life, Mia often received a gift and a letter from him every year on her birthday and also paid for her school tuition. However, Mia remained unaware of the truth that her father was actually royalty, the Crown Prince of the European country of Genvoia, making her a princess. Mia's family decided to keep the truth hidden from her and both her father and grandmother would keep their distance and not be involved to ensure Mia would have the chance of a normal life and planned to reveal the truth on her eighteenth birthday.
Mia lives in a renovated firehouse with her mother and pet cat, Fat Louie. Mia has a part-time job at the Falcon Sports Center for rock climbing and attends Grove High School with her best friend, Lilly Moscovitz, and her brother, Michael. Mia is viewed as invisible by the rest of the school and is often sat on by other students who never notice her presence. Mia is also frequently bullied and humiliated by popular girl and cheerleader, Lana Thomas, and her boyfriend, Josh Bryant, but despite their ridicule, Mia has harbored a longtime hidden crush on Josh.
Despite the struggles and hardships she faced, Mia was happy and content with her life and simply wished to get through high school with a minimum amount of attention and embarrassment as possible. In the months leading up to her sixteenth birthday, however, Mia's father died in a car crash. Despite never personally knowing him, Mia was left saddened by his death and was unaware that in the coming time, her life would soon change forever.
Mia is a fifteen-year-old private school student who lives with her mother, Helen, and her cat, Fat Louie, in a renovated San Francisco firehouse. Her father, Philippe Renaldi (who had divorced her mother years ago but still kept in touch with Mia) died two months earlier in a car crash. Although Mia is an average student, she is very unpopular but has two good friends: Lilly Moscovitz and her brother Michael (who harbors a crush on Mia). Her grandmother, Clarisse, contacts her for the first time, wishing to see her. During her visit, Clarisse reveals to Mia that she is the Princess of Genovia. Throughout the film, Mia struggles to balance her normal life with her princess responsibilities, making many mistakes and causing rifts between her and her friends, but she eventually manages to overcome these challenges once she discovers her father’s letter to her, encouraging her to accept her heritage and go to the ball Clarisse has planned for her. She accepts the title as the next heir of Genovia, and shares a kiss with Michael, officially becoming an couple.
In the sequel, Mia has graduated from college and turned 21. She returns to Genovia for her birthday and is revealed to have broken up with Michael, who left on tour with his band, therefore leaving the spot of her love interest open. At her 21st birthday party, she must dance with all the bachelors when a mysterious handsome man dances with her. Later, Mia is soon shocked to find out that she must marry someone in 30 days or she will not be able to rule Genovia as its queen as stated by law. She is upset. Her grandmother meets with Viscount Mabrey and his nephew, Nicholas, who is the man Mia met the night of her birthday and another heir for the throne. Clarisse invites Nicholas to stay. She is mad and steps on his foot and leaves. Her grandmother helps her find different suitors. Lilly, Mia, Charlotte, Clarisse, and Joe look through the different suitors and settle for one named Andrew Jacoby. Mia and Andrew meet and Mia thinks she likes him. They have a few more dates and then Andrew proposes to her and she accepts.
Although she is engaged to Andrew, Nicholas is flirting with Mia. At first he does it because his uncle who is Viscount Mabrey tells him to dissolve her engagement, but soon realizes he really likes her. The two kiss at the garden party and Mia's foot pops. She then runs away but Nicholas runs after and they fall into a fountain. Mia is later attempting to shoot arrows but doesn't do it right. Nicholas comes by whistling and Mia asks Lilly to distract Andrew so that she could talk to Nicholas. Nicholas helps her and her arrows go threw the ring. Nicholas tells Mia he came to pack up his things because he is leaving. Later that night, Nicholas is throwing pebbles at Mia's window and tells her to come down. She does and Lilly covers for her. They run off together on horses and find a nice place to stay by a lake. They talk, dance, and then fall asleep. The next morning, there is a man in a boat in the lake who was recording Mia and Nicholas. Mia thinks Nicholas set her up and runs away. The footage the man shot of her and Nicholas is already on TV when she gets back. She quickly goes to Andrew and says she is sorry. He grabs her and kisses her and admits she doesn't really feel anything when they kiss and he agrees. They then just decide that they made a commitment and are still going to get married for Genovia's sake.
The next day is the wedding day and Mia is very confused and nervous. She is waiting to walk down the aisle and Joe tells her that Nicholas didn't send the man that recorded them. Viscount Mabrey goes to the wedding while Nicholas debates if he should go or not, but decides against. After Viscount Mabrey leaves, their maid tells Nicholas that Viscount Mabrey sent the man who recorded him and Mia, and Nicholas leaves to the wedding on his father's bike. As Mia walks down the aisle, she stops and asks for a minute and runs out of the ceremony. Her grandmother runs after her and gives her the option to either go in there and get married or don't. And that it was her decision. She went back into the ceremony and said that she should be able to rule without a husband. Viscount Mabrey says that there must be a marriage otherwise Nicholas needs to be crowned King. Nicholas enters and declines the offer. Nicholas leaves and Vicount Mabrey goes after him. Almost everyone is the ceremony agrees that Mia should be able to rule without a husband. The next day is her coronation, she is sitting in a chair when Nicholas comes in and tells Mia that he is in love with her and asks and she loves him back and she runs over to him and hugs him and then they kiss and her foot pops again. The next scene is her coronation and Mia is officially crowned Queen Mia of Genovia.
- Mia has many differences between character in the original book and film series.
- In the original book series, Mia lives in Manhattan, not San Francisco. This was because Garry Marshall's granddaughters lived there, and he most likely did it out of respect for them.
- In the book series, Mia's surname is "Renaldo", not "Renaldi".
- In the book series, Mia's full name is Amelia Mignonette Grimaldi Thermopolis Renaldo.
- In the books, Mia's father is not only alive, but he is the one (not Clarisse) who tells her that she is a princess. She responds by running away to the penguin house in Central Park Zoo.
- In the book series, she marries Michael Moscovitz, Lilly’s brother who served as her love interest in the books and the first film, but in the film series, she has since then broken up with him by the time of The Princess Diaries 2: Royal Engagemeant and ends up with Lord Nicholas Devereaux instead. .
- She is a vegetarian and donates money to Greenpeace.
- Mia was actually the first Disney's princess to be crowned queen, the second being Princess Rosalinda from Princess Protection Program.
- In the first film, Anne Hathaway and Mia Thermopolis are 18 and 15 years old respectively, but by the sequel, they are both 21 years old.
- Her Genovian security code name is "Sparrow".