Ramón Gerardo Antonio Estévez, (born August 3, 1940) better known by his stage name Martin Sheen, is an actor best known for his performances as Captain Willard in the film Apocalypse Now and President Josiah Bartlet on the television series The West Wing. As well as the critical acclaim he has received as an actor, he has become known as an activist. Born and raised in Ohio, United States, with Irish and Spanish parents, Sheen is also an Irish citizen.

He is the father of actors Carlos Irwin Estévez (Charlie Sheen), Emilio Estévez, Ramón Estévez and Renée Estévez, and is brother of the actor Joe Estevez.

Sheen was born in Dayton, Ohio, the son of Mary Ann (née Phelan), an immigrant from Borrisokane, County Tipperary, Ireland, and Francisco Estévez, a factory worker/machinery inspector from Parderrubias, Galicia, Spain. Sheen's mother fought in the Irish War of Independence due to her family's connections to the Irish Republican Army. Sheen adopted his stage name in honor of the Catholic archbishop and theologian, Fulton J. Sheen. Sheen lived on Brown Street in the South Park neighborhood, and was one of 10 siblings (nine boys and one girl). One of his brothers is actor Joe Estévez. He attended Chaminade High School (now Chaminade Julienne Catholic High School) and was raised as a Roman Catholic.