Preston Parks
Preston Parks was a so-called faithless elector during United States presidential election, 1948.
A member of Tennessee Democratic Party, Parks was chosen by his Party as elector for Democratic nominees - Harry S. Truman and Alben W. Barkley. He, however, actively campaigned for Dixiecrats, a split group of segregationist Southern Democrats, who run their own (Strom Thurmond/Fielding L. Wright) ticket, opposing Truman's civil rights policy.
This made Parks the only elector pledged to one party, who campaigned for another ticket. Truman carried Tennessee but Preston, although formally pledged to him, cast his vote, as vowed, on Thurmond and Wright. Other Democratic Tennessee elector took the same pledge as Parks, but finally voted for Democrats.
Parks sole faithless vote, in addition to votes from States carried by Thurmond (South Carolina, Mississippi, Alabama and Louisiana), gave them total number of 39.