Mr. Morris has vowed to appeal SafeSport’s findings “regarding unsubstantiated charges for events that allegedly occurred between 1968 and 1972,” he said in a statement on Monday. “I have devoted my life to equestrian sport and the development of future riders, coaches and Olympians. Any allegations that suggest I have acted in ways that are harmful to any individual, the broader equestrian community, and sport that I love dearly are false and hurtful.”

Through his representative, Mr. Morris declined to be interviewed or to address any specific complaints about his relationships with riders.

The lifetime ban, which is reserved for the most egregious cases, according to SafeSport, comes on the heels of a wave of revelations about sexual abuse in the horse world. A 2018 Times investigation into Jimmy A. Williams revealed he molested several of the girls he trained over his nearly 40-year career. In June, after SafeSport barred Robert Gage, a trainer based in California, following an investigation into sexual misconduct, Mr. Gage killed himself.

The Times interviewed 53 former students, current top competitors and professionals, some of whom defended Mr. Morris and said they saw nothing untoward. Yet Mr. Morris’s relationships with minors were gossiped about from the warm-up ring to popular online message boards at Horse Show Diva and The Chronicle of the Horse.

Several people described Mr. Morris as consorting with underage students throughout his career, particularly during the 1970s. His behavior was waved away at the time as louche but acceptable, or the boys themselves were blamed or perceived as deliberately cultivating his attention for their gain.

Mr. Morris was born in New York City, but grew up in New Canaan, Conn., where he fell in love with horses, according to his memoir, “Unrelenting.” Mr. Morris came to national prominence when he won a team silver medal in Rome at the 1960 Summer Olympics. Later he became the United States equestrian team’s chef d’equipe — nothing less than its lodestar — leading the show jumpers to a team gold medal at the 2008 Beijing Olympics.