William Robert Greer (September 22, 1909 – February 23, 1985) was an Irish-born agent of the U.S. Secret Service, best known as being the driver of President John F. Kennedy's presidential limousine in the motorcade through Dealey Plaza in Dallas on November 22, 1963, when the president was assassinated.

Greer was born on a farm in Stewartstown, County Tyrone, Ireland, and emigrated to the United States in 1929.

During World War II, Greer enlisted in the U.S. Navy and was assigned to the presidential yacht in May, 1944.

[2] Greer retired on disability from the Secret Service in 1966 due to a stomach ulcer that grew worse following the Kennedy assassination.

Kellerman has stated that he shouted, "Let's get out of line, we've been hit," but that Greer apparently turned to look at Kennedy before accelerating the car.