He was an established matinee idol in his mid-thirties when he broke into films in 1915. After a career interruption caused by service in the cavalry in World War I, he returned to films as a popular leading man. Throughout the '20s, he was very busy onscreen playing dignified, well-mannered romantic heroes. For his work in The Patriot (1928), he received a Best Actor Oscar nomination. Stone's career remained very busy through the mid-'30s, and then continued at a slower pace through the early '50s; in the early sound era, when he was in his fifties, he played mature leads for some time before moving into character roles. Stone is best remembered as Judge Hardy, Andy's father in the Andy Hardy series of films with Mickey Rooney; typically, later in his career, he played Judge Hardy-like senior citizens. Ultimately, he appeared in over 200 films, almost all of them at MGM.