James Ronald Ryun (born April 29, 1947) is an American former Republican politician and Olympic track and field athlete, who at his peak was widely considered the world's top middle-distance runner. He won a silver medal in the 1500 m at the 1968 Summer Olympics, and was the first high school athlete to run a mile in under four minutes. He is the last American to hold the world record in the mile run. Ryun later served in the United States House of Representatives from 1996 to 2007, representing Kansas's 2nd congressional district.

According to Ryun, he began running because

I couldn't do anything else. When you're cut from the church baseball team, the junior high basketball team, and you can't make the junior high track and field team ... I'd go to bed at night and I'd say, "Dear God, please help me do better at sports and let me find a good sport I am good at" I found myself trying out for the cross-country team and running two miles even though I'd never run that distance before. All of a sudden, I made the team, I got a letter jacket, and I started thinking there's a girlfriend behind the letter jacket. But that's how it all began.

In 1964, as a high school junior at Wichita East High School, Ryun became the first high school athlete to run a mile in under four minutes in the time of 3:59.0, when he took eighth place at the 1964 California Relays, the last under four minutes in a historic mass finish under 4:00. His time of 3:55.3, set winning the 1965 AAU Championship race ahead of Olympic gold medalist and former WR holder Peter Snell, was a high school record that stood for 36 years. Ryun ran five sub four-minute miles while in high school including the first sub four-minute mile run in a high school event, a 3:58.3, at the 1965 Kansas HS state meet. As a high school senior, he was voted the fourth-best miler in the world by Track & Field News. ESPN.com named him the best high school athlete of all time, beating out people such as Tiger Woods and LeBron James. He was Track and Field News "High School Athlete of the Year" in 1965.

In 1966, at age 19, Ryun set two world records, first in the half-mile (1:44.9), then the mile (3:51.3). He received numerous awards, including Sports Illustrated magazine's "Sportsman of the Year" award, the James E. Sullivan Award as the nation's top amateur athlete, the ABC's Wide World of Sports Athlete of the Year award, and the Track & Field News' Athlete of the Year award as the world's best track and field athlete.

In 1967, Ryun set a world record in the indoor half mile (1:48.3) and the outdoor mile from (3:51.1), a record that stood for almost eight years. That same year, he set the world record for the 1,500 meters (3:33.1). In NCAA competition, Ryun was the 1967 NCAA outdoor mile champion. He was also the NCAA indoor mile champion in 1967, 1968, and 1969.

Ryun still holds the American junior (19 and under) records at one mile (3:51.3) and two miles (8:25.1). His American junior record in the 1,500 meters of 3:36.1 was broken by Hobbs Kessler on May 29, 2021, awaiting ratification by USA Track and Field. His American junior record in the 800 meters lasted exactly 50 years. In all, he broke the American record for the mile four times, once as a high school senior (3:55.3 on June 27, 1965), twice as a college freshman (3:53.7 on June 4, 1966, and 3:51.3 on July 17, 1966), and once as a college sophomore (3:51.1 on June 23, 1967).

Ryun participated in the 1964, 1968, and 1972 Summer Olympics. At age 17 years, 137 days in 1964, he remains the second youngest American male track athlete to ever qualify for the Olympics, behind Quincy Wilson. In 1968, he won the silver medal in the 1,500 meters in Mexico City, losing to Kip Keino from Kenya, whose remarkable race remained the Olympic 1,500-meter record for 16 years. Before the race, Ryun had thought that a time of 3:39 would be good enough to win in the high altitude of Mexico City. He ended up running faster than that with a 3:37.8, but half-way through the race Keino had moved into the first position at world record pace. Ryun continued to move up during the last two laps from eighth to second but was never closer than about 30 yards from Keino, who finished in 3:34.91, an Olympic record that would stand until 1984, despite the altitude. Years later, in 1981, he told Tex Maule in an interview for The Runner magazine, "We had thought that 3:39 would win and I ran under that. I considered it like winning a gold medal; I had done my very best and I still believe I would have won at sea level." Ryun was attacked by some writers who believed he had let his nation down. "Some even said I had let down the whole world. I didn't get any credit for running my best and no one seemed to realize that Keino had performed brilliantly." In the 1972 Munich, Germany, Games, he was tripped and fell down during a 1,500-meter qualifying heat. Although the International Olympic Committee (IOC) acknowledged that a foul had occurred, U.S. appeals to have Ryun reinstated in the competition were denied by the IOC.