Franklin Mieuli, the unconventional and popular owner of the Golden State Warriors for nearly a quarter century who in 1975 brought the franchise its only National Basketball Association championship in nearly 40 years on the West Coast, died Sunday. He was 89.

The death was announced by the Warriors, who said he died of natural causes in the Bay Area. A local boy who made good, Mieuli, grew up in San Jose and ran a successful radio production company. He bought a partial stake in the Warriors when the team moved to the Bay Area from Philadelphia in 1962 (taking with them the star center Wilt Chamberlain) and became a majority shareholder shortly thereafter.

Though it played its home games in several arenas throughout the Bay Area — most frequently at the Cow Palace, in Daly City — the team was called the San Francisco Warriors throughout the 1960s. Mieuli moved the team to Oakland in 1971 and changed its name to the Golden State Warriors; he sold the team in 1986.

Often referred to as eccentric, Mieuli eschewed business dress and grooming; heavily bearded, he favored jeans, Hawaiian shirts and a deerstalker cap, a la Sherlock Holmes. When events became too complicated and he needed time to think or to avoid the press, he would simply disappear for a few days. He kept a number of motorcycles, his preferred mode of transportation, and occasionally forgot where he left them.

“I had too many motorcycles and too short a memory,” he recalled in a 2008 interview with The San Francisco Chronicle.

He was, however, cagey and self-aware.

“Make no mistake,” Hank Greenwald, a former Warriors radio announcer, said in a 1971 Sports Illustrated article about Mieuli, “Franklin is the one man in the world who works hard at having people underestimate him.”

He was not an owner with especially deep pockets, and his stewardship of the Warriors sometimes appeared quixotic. With the team in a financial bind in 1965, he traded Chamberlain back to Philadelphia, where the Syracuse Nationals had moved and become the 76ers.

“I don’t mean that I personally dislike him,” Mieuli said of Chamberlain after the trade. “He’s a good friend of mine. But the fans in San Francisco never learned to love him. I guess most fans are for the little man and the underdog, and Wilt is neither. He’s easy to hate, and we were the best draw in the NBA on the road, when people came to see him lose.”

Mieuli opposed league expansion and opposed the merger of the NBA with its rival league, the American Basketball Association. (After years of negotiations, the merger took place in 1976.) He opposed the 3-point shot. He pursued the star forward Rick Barry as if he were a long-lost son, signing him out of college in 1965, losing him to the ABA two years later and re-signing him in 1972.

Barry went on to lead the Warriors’ 1975 championship team in scoring with an average of 30.6 points per game.

Mieuli, a son of Italian immigrants, was born on Sept. 14, 1920, in San Jose, Calif., where his father was a gardener who eventually started a successful nursery. He attended the University of Oregon and served in the Navy during World War II.

He worked in marketing for a local brewery, sponsor of radio broadcasts of San Francisco 49ers football games. In 1954, according to the team, he produced the first telecast of a 49ers game. He subsequently bought a small share of the team, and a few years later, having entered the radio and television production business himself, he landed the rights to produce not only their games but also those of the newly arrived major league baseball franchise, the San Francisco Giants. At his death, he retained a 5 percent interest in the 49ers.

Mieuli’s marriage ended in divorce, and he had a long partnership with Blake Green. His survivors include Green, three children and seven grandchildren.