Masaccio (Italian pronunciation: [maˈzattʃo]; December 21, 1401 – autumn 1428), born Tommaso di Ser Giovanni di Simone, was the first great painter of the Quattrocento period of the Italian Renaissance. According to Vasari, Masaccio was the best painter of his generation because of his skill at recreating lifelike figures and movements as well as a convincing sense of three-dimensionality. Masaccio died at twenty-six and little is known about the exact circumstances of his death.

The name Masaccio is a humorous version of Maso (short for Tommaso), meaning "clumsy" or "messy" Tom. The name may have been created to distinguish him from his principal collaborator, also called Maso, who came to be known as Masolino ("little/delicate Tom").

Despite his brief career, he had a profound influence on other artists. He was one of the first to use Linear perspective in his painting, employing techniques such as vanishing point in art for the first time. He also moved away from the International Gothic style and elaborate ornamentation of artists like Gentile da Fabriano to a more naturalistic mode that employed perspective and chiaroscuro for greater realism.