Rafer Johnson, who carried the American flag into Rome’s Olympic Stadium in August 1960 as the first Black captain of a United States Olympic team and went on to win gold in a memorable decathlon duel, bringing him acclaim as the world’s greatest all-around athlete, died on Wednesday at his home in the Sherman Oaks section of Los Angeles. He was 86.

Michael Roth, a family friend and spokesman, confirmed the death.

Johnson never competed after that decathlon triumph. He became a good-will ambassador for the United States and a close associate of the Kennedy family, taking a leadership role in the Special Olympics, which were championed by Eunice Kennedy Shriver, and joining Robert F. Kennedy’s entourage during Kennedy’s presidential campaign in 1968. He was remembered especially for helping to wrestle the senator’s assassin to the ground in Los Angeles in 1968.

Johnson’s national profile was largely molded at the 1960 Olympics, one of the most celebrated in the history of the Games, a moment when a host of African-American athletes burst triumphantly onto the world stage. Muhammad Ali, known then as Cassius Clay, captured boxing gold in the light-heavyweight division.

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Wilma Rudolph swept to victory in the women’s 100- and 200-meter dashes and combined with her Tennessee State teammates for gold in the 4-x-100 relay. Oscar Robertson helped take the United States basketball team to a gold medal.

Johnson’s narrow decathlon victory over C.K. Yang of Taiwan and U.C.L.A., a good friend, provided a thrilling moment in its own right.

Johnson, a 25-year-old graduate of U.C.L.A. and a chiseled 6 feet 3 inches and 200 pounds, was the favorite going into the two-day decathlon, a 10-event test of versatility, strength, speed and endurance that included sprints, high hurdles, pole-vaulting, the high jump and broad jump, the javelin and discus throws, and the 1,500-meter run.

He had won silver in the decathlon at the 1956 Melbourne Olympics, finishing behind Milt Campbell of the U.S., who turned to pro football afterward. He had bested Vasily Kuznetsov of the Soviet Union at a meet at Lenin Stadium in Moscow in 1958, inspiring spectators to put aside Cold War issues and cheer his achievement. And he scored a world-record 8,683 points in the decathlon at the 1960 Olympic track and field trials in Oregon.

But he faced a stiff challenge in Rome from the 27-year-old Yang, who was representing Formosa, the Olympic designation at the time for Taiwanese athletes. Both were trained by Elvin Drake, known as Ducky, the U.C.L.A. track and field coach.

The decathlon duel was decided in its final event, the 1,500 meters, in which Yang was especially strong. Johnson, leading on points, didn’t have to win the event to capture the gold medal, but he did need to finish within 10 seconds of Yang.

“I planned to stick with him like a buddy in combat,” Johnson told The Los Angeles Times in 1990. “I had one other advantage, and I don’t think C.K. knew this at the time. This was my last decathlon. I was prepared to run as fast as I had to in this last race of my life.”

Yang, who died in 2007, recalled, “I knew he would never let go of me unless he collapsed.” Johnson finished 1.2 seconds behind Yang, good enough to capture gold, with Yang getting silver and Kuznetsov capturing bronze.

Johnson later received the 1960 Sullivan Award as America’s leading amateur athlete. After that, he embarked on new chapters in his life.

He met Robert Kennedy at an awards ceremony soon after the Rome Games and became part of the senator’s campaign for the 1968 Democratic presidential nomination.