Donald Rex Clark (December 22, 1923 – August 6, 1989) was an American football player and coach who was perhaps best known as the head coach of the USC Trojans football team from 1957 to 1959. He compiled a 13–16–1 record while coaching at USC, going 0–5–1 against rivals UCLA and Notre Dame. The highlight of his career was in 1959, when USC shared the inaugural AAWU title in a three-way tie. However, he remains the only coach to post a losing record at USC over more than one season.