After watching the Seattle Opera present it in 1975, Sloan eventually experienced all 15 hours of the musical drama 90 times.
Back in Los Angeles as a fledgling "Ring" fanatic, he listened to it so much that his teenage children gave him an ultimatum, he told The Times in 2003: They said, "It's either 'The Ring' or us, and I said I'll help you pack.' Next day, they bought me earphones."
Sloan, who co-founded the Wagner Society of Southern California nearly 30 years ago, had long wanted to see the epic opera staged in Los Angeles. On Saturday, Los Angeles Opera began unveiling its first complete performance of "The Ring," but Sloan was too ill to attend.
On Monday, he died of pneumonia at Hollywood Presbyterian Medical Center, his family announced. He was 72.
"He was a true friend to L.A. Opera, one of the company's most enthusiastic supporters since our earliest days," Placido Domingo, the opera company's general director, said in a statement. "I am particularly saddened that he was not able to see the L.A. 'Ring,' which he had been anticipating for so many years."
To many, Sloan was perhaps the ultimate Wagnerite, leading fans on tours of opera houses around the world and genially hosting meetings of the Wagner society at his home beneath the "D" of the Hollywood sign, where "a panoramic view of the city was almost as great an attraction as the music," said Gerald Faris, a friend.
A board member of L.A. Opera and the Opera League of Los Angeles, Sloan filled a crucial role for both as an opera educator, said Nick Ciriello, who was on the L.A. Opera board.
"He was very important to educating the audience about opera, scheduling lectures and seminars," Ciriello said. "And he is really responsible for the cause of Wagner … in the Southland."
After Sloan and his wife, Irene, started the society in 1982, he chaired it for years as the group grew to 300 members. In 1983, the Sloans also founded the Opera Quarterly, an academic journal that is still published. The couple later divorced.
A highlight of Sloan's year, friends said, was the annual trip he led to Bayreuth, Germany, the original home of Wagner's cycle of four operas that is formally known as "Der Ring des Nibelungen."
When asked if he ever tired of sitting through the mythic saga — which tells the story of the beginning and end of the world, complete with dwarfs and Valkyries — Sloan told The Times "no" in 1998 by recalling a trip to Munich: "Once I went to a 'Ring,' which takes a week, and I stayed and saw it all over again."
Sherwin H. Sloan was born March 28, 1938, in Chicago to parents who ran a neighborhood market.
In high school, he played the cello and became hooked on opera while listening to Saturday morning radio broadcasts of the New York Metropolitan Opera.
After moving to Los Angeles with his family, Sloan earned a bachelor's degree from the University of Arizona and graduated from UCLA's medical school.
While in private practice in Encino and Ventura, he was chief of ophthalmology at Sepulveda Veterans Medical Center and taught at UCLA's Jules Stein Eye Institute.
When Sloan retired in early 1998, he was looking forward to seeing his 48th "Ring," in Arizona that summer.
Sloan is survived by Robert Torres, his partner since 1998; two children, Kathy of Highland, Calif., and Jeffrey of Irvine; a brother, Dr. Allen Sloan, an optometrist, of Woodland Hills; and a sister, Elyse Papke, of Loudon, Tenn.
The Sunday L.A. Opera performance of "Gotterdamerung," which marks the end of the first "Ring" cycle presented in Los Angeles, will be dedicated to Sloan.
A memorial will be held at 5:15 p.m. June 13 on the fifth floor of the Dorothy Chandler Pavilion, 135 N. Grand Ave., Los Angeles.