Ryun, RY uhn, Jim (1947-...), an American track star, became the world's fastest middle-distance runner. In 1966, he set a record by running the mile in 3 minutes 51.3 seconds. Ryun set another record that year by running 880 yards in 1 minute 44.9 seconds. In 1967, he set a 1,500-meter record of 3 minutes 33.1 seconds and lowered his mile record to 3 minutes 51.1 seconds. Other runners later broke Ryun's records.