Robert Allen O'Brien
- Bats Left, Throws Left
- Height 5' 10", Weight 170 lb.
- School Fresno City College, Texas A&M University, University of Arizona
- Debut April 11, 1971
- Final Game July 7, 1971
- Born April 23, 1949 in Pittsburgh, PA USA
O'Brien, who had been at the University of Arizona in 1968, was drafted by the Dodgers in the 4th round of the January 1969 amateur draft and went 11-3 for the Ogden Dodgers in 1969 and 13-3 for the Spokane Indians in 1970. He made his major league debut in April 1971, in a game started by Don Sutton.