“It’s who we are,” Mr. Toussaint said of New Orleans, in an interview last year published by the Red Bull Music Academy. “The food we eat, the history, Mardi Gras Indians who rehearse all year around, the second-line brass bands who strut that stuff, the syncopation, the humor, and the slightly slower pace than the rest of America — the way we mosey along rather than running the race.”

On Tuesday Paul Simon, with whom Mr. Toussaint was scheduled to give a benefit concert in New Orleans on Dec. 8, recalled their long history together, which goes back to recording sessions in the early ’70s, when Mr. Toussaint played piano for him and wrote chord charts for his musicians.

“We were friends and colleagues for almost 40 years,” Mr. Simon wrote in an email. “We played together at the New Orleans jazz festival. We played the benefits for Katrina relief. We were about to perform together on Dec. 8. I was just beginning to think about it; now I’ll have to think about his memorial. I am so sad.”

Allen Toussaint was born on Jan. 14, 1938, in Gert Town, a working-class neighborhood of New Orleans, to Clarence Toussaint, a railway worker, and the former Naomi Neville, whose names he occasionally used as songwriting pseudonyms. By his early teens he was playing piano with the guitarist Snooks Eaglin, and he got his first break when he substituted for the New Orleans bandleader and pianist Huey Piano Smith on tour in 1957.

The next year, Mr. Toussaint recorded “The Wild Sound of New Orleans,” an album of instrumentals released by RCA Victor under the name Tousan. It was no hit, but it later gave him a taste of success as a songwriter: One song on the album, “Java” — for which Mr. Toussaint shared credit with Alvin Tyler and Freddy Friday — was covered by the trumpeter Al Hirt in 1963 and reached No. 4 on the Billboard pop chart.

In 1960, Mr. Toussaint became the house producer, arranger and songwriter for the Minit label, where he worked with Irma Thomas, Aaron Neville, Benny Spellman and others. After serving in the Army from 1963 to 1965, he returned to music, establishing Sansu Enterprises, a publishing company and group of record labels, with Mr. Sehorn.