(CNN) -- American fitness guru Jack LaLanne died Sunday afternoon at his home in Morro Bay, California, according to his long-time agent, Rick Hersh. He was 96.

The cause, said Hersh, was respiratory failure due to pneumonia. LaLanne had been ill for the past week. His wife, Elaine, was at his side, along with his family and friends, Hersh said. No funeral arrangements were announced, but his agent said plans were being made.

LaLanne spent decades talking about the healthful benefits of exercise and fitness. He opened his own health spa in California in 1936, years before the fitness craze swept the United States. LaLanne even designed the world's first leg-extension machine, along with several other pieces of fitness equipment now standard in the fitness industry.

He was born in San Francisco on September 26, 1914. A self-confessed sugar- and junk-food addict as a child, he went on to study bodybuilding and weight-lifting by the time he was in his late teens.

From the 1950s through the 1980s, LaLanne performed multiple feats of strength and endurance. His first such stunt was an underwater swim the length of the Golden Gate Bridge, loaded with 140 pounds of equipment, in 1954. He went on to stage many attention-getting events, including completing over a thousand pushups in a little over 20 minutes, and towing 65 boats filled with thousands of pounds of wood pulp in Japan.

LaLanne had his own workout program, "The Jack LaLanne Show." First broadcast nationally in 1959, the show went on to run for three decades.

In his later years, he was easily recognized because of late-night infomercials on on the benefits of juicing.

He also made many appearances on CNN's "Larry King Live" and was a friend of the talk show host. "There was no one like Jack LaLanne," King said Sunday night. "He would go on forever ... a true guru. I guess Charles Atlas from the old comic books would be the predecessor for Jack LaLanne."

But it wasn't simply LaLanne's physical prowess that impressed King. "Elderly people were encouraged by him because he just kept on going," King said, adding that modern fitness celebrities owe a debt of gratitude to the original impresario of exercise.

LaLanne's wife of 51 years released a statement on her husband's passing: "I have not only lost my husband and a great American icon, but the best friend and most loving partner anyone could ever hope for," Elaine said.

CNN's Chuck Johnston contributed to this report