It's not every day that you lose your curator of just about everything except the kitchen sink (and maybe that, too).

But, then again, Joseph Rishel is not actually leaving the Philadelphia Museum of Art.

After 41/2 decades, much of it spent with the august title of Gisela and Dennis Alter senior curator of European painting before 1900, the John G. Johnson Collection, and the Rodin Museum, Rishel has retired.

He's now simply emeritus curator of European painting - a curator who comes in at 10 in the morning, not 9, and doesn't wear a tie, he says.

To honor his long and important tenure, the museum is holding an invitation-only celebration Sunday evening, an event marking the 76th birthday of a man who has overseen and guided a major portion of the museum's collections from deep in the 20th century to well into the 21st.

He has worked to change the profile of the museum and how it relates to the city, and he has launched a whole generation of curators and museum directors to positions of significance all over the country.

"Joe is the best," said museum director Timothy Rub, in a judgment echoed by colleague after colleague.

"People are exceptionally fond of him," Rub said. "They also immensely admire the work he's done over a long and distinguished career. He's just a great person to work with."

Since he arrived at the museum in 1971 as associate European art curator - joined shortly thereafter by his new bride, Anne d'Harnoncourt, who had been recently named the museum's associate curator of modern art - Rishel's curatorial expertise, his vast and eclectic knowledge of art history, and, perhaps most of all, his inquisitive and genial nature have helped transform the entire museum.

Rishel met his future wife when both labored at the Art Institute of Chicago. In 1972, Rishel was named Philadelphia's curator of European art and d'Harnoncourt took the reins of 20th-century art, becoming museum director in 1982; she died in 2008.

"He functioned almost as a chief curator," said Alice Beamesderfer, deputy director for collections and exhibitions, who has known Rishel for 30 years. "He was the person the entire curatorial team turned to."

Rishel made his first big splash in typical fashion - a huge, smorgasbordian exhibition that had some scratching their heads in advance.

But after the Second Empire: Art in France under Napoleon III opened in 1978, there was no more head-scratching.

Poet and critic John Ashbery, writing in New York magazine, characterized the show, the largest in museum history at that time, as "stunning."

"It's hard to think of a recent art event where so much seriousness has resulted in so much fun," Ashbery wrote, rhapsodizing over juxtapositions of painting, photography, architecture, decorative arts, and even wallpaper.

He could have been talking about the curator himself.

Rishel cast a wide net in Second Empire, as he has done repeatedly since in shows addressing, for instance, 18th-century Rome and Latin American art, all put together with teams of curatorial collaborators.

"Everything was in some fashion or other a collaboration, absolutely everything," the emeritus curator said, looking back on his career. "So much of my life has been a question of collaboration."

Rishel is probably best known for the Cézanne exhibition, the 1996 show that is still the best-attended in the museum's history.

"In terms of new scholarship about Cézanne, it was a game-changer," Beamesderfer said. "It was also a game-changer in civic terms. The city realized how powerful the museum could be in terms of economic development."

He would return to Cézanne in subsequent exhibitions. Prior to the opening of Cézanne and Beyond in 2009, Rishel was asked what is there left to say about the artist. He chuckled. "Cézanne is like a fine ham. You can keep slicing and slicing and slicing."

(He proved that point with 2012's Gauguin, Cézanne, Matisse: Visions of Arcadia; and he's still ruminating about possible Cézanne pairings. Jasper Johns, anyone?)

Rishel has also had an enormous impact on the permanent collection of the museum.

He rethought and reinstalled the museum's great John G. Johnson collection during the mid-1990s and is now working on an exhibition to mark the centennial of Johnson's 1917 death.

His friendship with collectors has proved invaluable. He shepherded Henry McIlhenny's bequest of works by David, Delacroix, and Ingres, among others, into the museum's collection, for instance.

"For this wonderful bon vivant, happiness was so much involved with the buying of art and the showing of it," Rishel said.

Rishel also was critical in bringing the recent bequest of Helen Tyson Madeira's paintings into the museum's collection in 2014 - with Cézanne's Mont Sainte-Victoire a notable highlight.

And then there are his colleagues. Many of the men and women Rishel has worked with over the years are now running their own museums or guiding their own collections.

"Joe is an amazing figure in the city's cultural life," said William Valerio, who was in charge of the museum's government relations in the early 21st century and has headed the Woodmere Art Museum since 2010. "Joe as a curator was a great team builder. Everyone wanted to be a part of it. It was exciting. He would wrap his arms around you."

"He treated his department as a team," Valerio continued. "Everyone could hear everyone's conversations. Everyone could hear the phone calls Joe was making. That structure really worked. He has a magnetism and a charisma that's unique."

Peter C. Sutton, who served as an assistant curator for European art at the museum from 1979 to 1984, characterized Rishel as "a great inspiration." Sutton went on to become director of the Wadsworth Atheneum in Hartford, Conn., and is now head of the Bruce Museum of Arts and Science in Greenwich, Conn.

"I truly regarded Joe as a mentor, and he was very funny. I couldn't get anything done I laughed so much. Anne finally moved me to another office. Joe told such funny stories. . . . But he took a lot of us under his wing for a while and taught us how to be a curator. I owe a huge debt to Joe. He was the model curator."

That assessment is shared by younger art museum curators to this day.

"Joe is really gregarious," said museum photography curator Peter Barberie. "I think of him as a true museum guy. He is all about museums. . . . He is interested in what everybody is doing. He's very supportive and very broad-minded about what can happen in a museum."

"People just adore him."