CHICAGO — Johnny Bach, whose defensive expertise as an assistant coach to Phil Jackson helped the Chicago Bulls win three NBA titles from 1991 to 1993, has died. He was 91.

The Bulls confirmed the death yesterday.

Bach was the head coach of the Golden State Warriors from 1983-86 before joining the Bulls as an assistant. He also worked as an assistant for Charlotte, Detroit and Washington. He returned to the Bulls in 2003 and retired in 2006 after more than a half-century in coaching.

“Johnny was a true treasure in the world of basketball,” Chicago executive vice president of basketball operations John Paxson said in a statement. “He was the classic ‘old school’ coach who came to work each and every day with energy and enthusiasm for the game he loved. His zest for life and basketball were unparalleled.”

Paxson played for the Bulls when Bach was an assistant with Chicago.

Bach was the coach at Fordham from 1950-68 and at Penn State from 1968-77. He also served as an interim coach for the Warriors for 21 games in 1979-80.

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“The Golden State Warriors are saddened by the passing of John Bach today at the age of 91,” the Warriors said in a statement. “A veteran of World War II, Bach spent more than 55 years of his life in the coaching profession at the collegiate and professional levels. Our deepest condolences go out to Bach’s family and friends.”

Bach played at Fordham both before and after serving in World War II. He played briefly for the Boston Celtics in the NBA before eventually returning to Fordham as coach.

Bach was an assistant on the U.S. coaching staff at the 1972 Olympics, where the Americans lost the title game to the Soviet Union in controversial fashion.

“John Bach was a defensive mastermind who coached and inspired so many greats,” Penn State coach Patrick Chambers said. “His teams at Penn State in the 1970s were known for their toughness and attitude.”