Mia Thermopolis is a fictional character from the young adult series written by Meg Cabot. She is introduced in the book "The Princess Diaries," where she discovers that she is the heir to the throne of the fictional European country of Genovia. Mia is portrayed as a relatable teenager who navigates the challenges of adolescence while dealing with her unexpected royal status. Throughout the series, Mia faces various personal and social issues, including friendships, romance, and self-acceptance. Her character is known for her quirky personality, diary entries, and growth as she learns to embrace her identity as a princess while remaining true to herself.