Wolfgang Wagner took over the festival with his brother in 1951
Wolfgang Wagner, former director of the Bayreuth Festival and the grandson of composer Richard Wagner, has died aged 90 in Germany.
A statement on the festival's website said that Wagner died on Sunday, but did not give further details.
"Wolfgang Wagner dedicated his whole life to the legacy of his grandfather," the festival website said.
Wagner stepped down as the event's director in 2008 after leading it for for more than half a century.
Born on 30 August 1919 in Bayreuth, Wagner studied the trumpet and French horn before being sent to fight on the eastern front early in World War II.
He first took charge of the festival dedicated to his grandfather's works in 1951, first with his brother Wieland, and then as the sole director from 1966 - with a lifetime contract.
In addition to increasing the funding and establishing a separate foundation to oversee the composer's library, Wagner also invited directors from abroad to direct individual operas.
Katharina Wagner and Eva Wagner-Pasquier are joint directors
While many of the versions sparked controversy at the time, they were often groundbreaking interpretations of Richard Wagner's operas, in keeping with his idea of broadening their meaning.
His insistence on serving out his lifetime contract led, in his later years, to a lengthy power struggle with officials who oversaw the annual summer event and also triggered a spat within the Wagner family.
For years, Wolfgang Wagner insisted that only his second wife, Gudrun, could replace him, although German government officials and others overseeing the festival refused to accept her.
By the time Gudrun died in November 2007, Wagner was insisting that only the couple's daughter, Katharina, could fill his shoes - putting him at odds with two other Wagners who also sought the job.
After Wolfgang stepped aside in 2008, Katharina and Wolfgang's long-estranged daughter from his first marriage, Eva Wagner-Pasquier, teamed up to beat out a rival bid from their cousin. They took charge of the festival last year.
Wagner is survived by his two daughters and a son, Gottfried. There were no immediate details of funeral arrangements.