George Christie, who inherited the mantle of caretaker of Glyndebourne, the stately English manor where he expanded beyond his family’s wildest ambitions the curious opera house his father had built, died May 7 at his home in East Sussex. He was 79.

A spokeswoman for Glyndebourne, Vicky Kington, confirmed the death but declined to disclose a cause.

To classical music fans, Glyndebourne is a beloved oddity, the home for the past 80 years to an intimate and celebrated opera festival that began in a display of spousal devotion.

John Christie, Mr. Christie’s well-to-do and eccentric landowning father, opened the opera house in 1934 with the assistance of his wife, Audrey Mildmay, a soprano who became one of the first singers to perform there. (She was pregnant with George at the time.)

From the beginning, there were few other places in the world like Glyndebourne — a theater attached to a family residence and surrounded by gardens where patrons could indulge in picnics and champagne.

George Christie, who led the Glyndebourne opera festival for more than four decades, died May 7 at 79. (Photo by Chris Cormack )

In time, Glyndebourne’s charms and reputation for artistic quality drew increasingly large audiences from the British upper crust. While diminutive in size — John Christie’s original house seated 300 — the enterprise was grandiose in aspirations and showcased stars including Luciano Pavarotti, Ruggero Raimondi, Montserrat Caballé and Frederica von Stade.

John Christie led the operation until 1958, when George, then 23, took over. He recognized the opera house’s shortcomings, including acoustics that reminded one British critic of being “shut up in a matchbox with a bumblebee.” Mr. Christie also understood that the house was too small to accommodate audiences large enough to cover opera’s growing costs.

By the early 1990s, he had decided to remedy both problems with the construction of an entirely new, dramatically larger theater.

“This theater is ill-designed, and the general fabric has reached its sell-by date,” Mr. Christie told the Chicago Tribune. “I have a nostalgic love for the place, but I desperately want to see a better theater here for the longer term. I don’t see Glyndebourne surviving without that.”

Mr. Christie engaged Michael and Patty Hopkins, a husband-and-wife architectural duo, to design a new theater. The facility opened in 1994 at a reported cost of $50 million from private donors. The new construction was widely acclaimed and seats up to 1,200.

Once the home of classic works by composers such as Mozart, the opera house became under Mr. Christie’s leadership a showcase for modern or avant-garde operas such as Alban Berg’s “Lulu,” Leos Janacek’s “The Makropulos Case” and George Gershwin’s “Porgy and Bess.”

There were flops, including an unpopular Peter Sellars production of Mozart’s “The Magic Flute” that placed the story in Los Angeles. And while some patrons regarded the Glyndebourne milieu as elegant, others found it stodgy.

“Black tie is ‘recommended,’ not obligatory for men, but woe betide anyone who turns up in mufti,” a writer noted in the Sunday Times of London. “The looks you get from the assembled penguins are withering.”

Mr. Christie worked to broaden Glyndebourne’s reach by starting a touring opera company in the late 1960s. He also was credited with expanding the theater’s accommodations to include standing room and restricted-view seats for opera lovers who lacked funds for finer perches.

He rejected the notion that Glyndebourne was simply a place to see and be seen for the rich and elite.

“They haven’t gotten where they are without formidable intelligence,” Mr. Christie said of his wealthier audiences. “They are by far and away the most adventurous end of the audience. They come to see a newly commissioned, contemporary piece, where the individual member will not.

“It seems to me that the Glyndebourne audiences have no more ill-educated nincompoops than any other opera audience,” he continued. “This attitude that they do has been fostered by the press, which regards people having wealth as being stupid.”

George William Langham Christie was born Dec. 31, 1934, at his parents’ home on the Glyndebourne estate.

He studied at Trinity College at the University of Cambridge before taking his position with Glyndebourne. He was knighted in 1984 and, upon his retirement in 1999, was succeeded by his son Gus.

Survivors include his wife of 55 years, the former Patricia Mary Nicholson of East Sussex; four children, Hector Christie of Devon, England, Augustus Christie of the Glyndebourne estate, and Ptolemy Christie and Louise Flind, both of East Sussex; and 11 grandchildren.

Upon his death, Mr. Christie was widely praised in the British media for having shared his family’s artistic riches with the public. He had grown up in a world where it was normal to have an opera house attached to one’s home — and to allow others to partake in its pleasures — and his children appeared to have been raised in the same spirit.

“Thank you for having me,” his son Hector was said to have told a friend who invited him over to play. Hector added, “Before I go can I have a look at your opera house?”