Muscular, barrel-chested, yet sensitively talented silent star whose breakthrough came with the lead role in John Ford's "The Iron Horse" (1924). O'Brien starred for Fox Studios in many films after that, reuniting with Ford for such films as "The Fighting Heart" (1925) and "Three Bad Men," as well as playing in Howard Hawks' dated but amusing marital farce "Fig Leaves" (1926). 1927 saw O'Brien give an excellent performance in the greatest and most famous film of his career, F.W. Murnau's classic "Sunrise" (1927). He made a successful transition to sound soon thereafter, and began playing tough but good-humored heroes in many enjoyable B-budget Westerns including "Riders of the Purple Sage" (1931) and "Mystery Ranch" (1932). Ending his dozen years with Fox, O'Brien moved over to RKO for "Daniel Boone" (1936), "Border G-Man" (1938), and "Racketeers of the Range" (1939), among others. He made few film appearances after the advent of WWII, though he was most welcome in small roles in Ford's "Fort Apache" (1948) and "She Wore a Yellow Ribbon" (1949) and made his last film (and the last of 11 with Ford) in 1964, "Cheyenne Autumn."