Paul Edward Valentine Giamatti (born June 6, 1967) is an American actor and comedian. He began his career as a supporting actor in several films produced during the 1990s including Private Parts, The Truman Show, Saving Private Ryan, The Negotiator, and Man on the Moon, before earning lead roles in several critically acclaimed projects in the 2000s including American Splendor, Sideways, Cinderella Man, and John Adams.

Giamatti was born and raised in New Haven, Connecticut. His father, A. Bartlett Giamatti, was a Yale University professor who later became president of the university and commissioner of Major League Baseball. His mother, Toni Smith, was a homemaker and English teacher who taught at Hopkins School and had also previously acted. Giamatti's mother was Irish American; his paternal grandfather, Valentine Giamatti, was an Italian American, of parentage from Telese, and his paternal grandmother was Mary Claybaugh Walton, whose ancestors lived in the United States.

Giamatti has a brother, Marcus, who is also an actor. Giamatti attended The Foote School, then the elite boarding school Choate Rosemary Hall. He attended Yale University, where he was active in the undergraduate theater scene and worked alongside actors Ron Livingston and Edward Norton, who were also Yale students. He graduated from Yale in 1989 with a bachelor's degree in English. He went on to earn a Master's degree in Fine Arts from the Yale School of Drama where he studied with Earle R. Gister. He performed in numerous theatrical productions (including Broadway) before appearing in some small television and film roles in the early 1990s. In Giamatti's junior year at Yale he was "tapped" to enter Yale's elite and clandestine Skull and Bones secret society.