Les Mills, an Olympian for New Zealand who founded and gave his name to a family-owned fitness empire that helped popularize aerobics, died on Monday. He was 91.

Les Mills International, the company he founded, announced the death but provided no further details.

The company made its name by promoting vigorous group aerobics sessions set to upbeat music, helping to popularize the exercise format in New Zealand, and then around the world.

Leslie Roy Mills was born Nov. 1, 1934, in Auckland, New Zealand. His father, who owned butcher shops, died when Les was 11.

Mr. Mills competed in shot put and discus and participated in four Olympic Games from 1960 to 1972. His best finish was seventh in the shot put in 1964. He was chosen to carry the New Zealand flag at opening ceremonies in 1960 and 1972. He won the discus competition at the 1966 Commonwealth Games.

In an era when Olympic sports were strictly amateur, he opened a shoe shop in New Zealand at age 19 with his wife Colleen, also a track athlete. In the middle of his athletics career, he spent two years competing for the University of Southern California and was inspired by the area’s emerging gym culture.

He founded his first gym in 1968 in Auckland. It was so small that it had just one changing area and bathroom, so it was open to men and women on alternate days, the company said.

As the gym business grew into Les Mills World of Fitness, it began pioneering aerobics with group classes set to peppy music that were given names like BodyPump and BodyAttack,

His son Phillip turned Les Mills New Zealand into Les Mills International and it has since spread to 100 countries.

His wife Colleen died in 2005. Mr. Mills is survived by Phillip and a daughter, Donna; four grandchildren; and great-grandchildren. Both his children competed in track and field at the Commonwealth Games.

After his athletics career, Mr. Mills became national sports director in Papua New Guinea from 1974 to 1976, leading the country to its first Olympics. He also was a coach with the New Zealand track team and coached Beatrice Faumuina to the 1997 world discus title.

He was elected mayor of Auckland City, serving from 1990 to 1998. He was named a member of the Order of the British Empire in 1973 and Companion of the New Zealand Order of Merit in 2002.

“I think he saw the gym as a place where people could come and find refuge, could improve their lives and get healthier and find community and all those nice things,” Phillip Mills told RNZ, a New Zealand public broadcaster. “And I think he would have liked to have seen a little bit more of that in the world today.”