In 1938, Jelly Roll Morton sat down with Library of Congress folklorist Alan Lomax for a legendary dialogue, which was both performance and oral history.

It’s an astonishing set of recordings — both an intimate conversation and a fabulous show — that includes tale-spinning, historical detail, saucy language, dirty blues and complex improvisations on the piano. (The full sessions, which span nine hours over seven discs, were made available as a boxed set put out by Rounder Records in 2005.)

The sessions also contain what most scholars say is the first recording of Mardi Gras Indian music, as well as the first documented revelation of Indian culture and practices to an outside scholar.

Over about four minutes, Morton wove a vibrant image of a gang of Indians out at Mardi Gras:

“Even when the parades that cost millions of dollars would be coming along, if a band of Indians was coming, why, the parade wouldn’t have anybody there,” he said. “They would flock to see the Indians. They would dance, and sing, and they would go on just like regular Indians. They would be armed with fictitious spears and tomahawks, and incidentally, some of them would sometimes break the rules and have some real material to fight with.”

Events were held this week to celebrate Morton’s birthday, which scholars generally agree is Oct. 20, though there is debate about whether the pianist was born in 1885 or 1890.

Bruce Raeburn, the director of Tulane University’s Hogan Jazz Archive, hosted an informal listening session and talk about Morton, a figure who remains nearly as complex as he was influential. Tom McDermott also played a set of Morton’s music at a commemoration at Snug Harbor.

During his lifetime, Morton was flamboyant — a whorehouse entertainer and alleged pimp with a diamond tooth and a large wardrobe of flashy suits. He was born Ferdinand Joseph Lamothe, a Creole of color, but changed his stepfather’s last name — Mouton — to Morton and took on a nickname that, at the time, was slang for genitalia.

“He was a pimp, a pool hustler, a card shark and a braggart, with a diamond tooth and all the extramusical stuff, there’s that,” said McDermott. “He’s fascinating to people because of his bizarre life story. But also, if you’re attuned to the music of that period — it helps if you know ragtime, and classical — when you hear Morton it’s as much of a shock as (James) Booker or Professor Longhair, as big of a jolt to your system. He’s not given his due as the guy who came the closest to inventing jazz; he was the first great jazz composer.”

To pay homage to the pianist, Irvin Mayfield’s New Orleans Jazz Orchestra opened its fall concert season on Friday with a tribute to Morton’s music at the People’s Health Jazz Market on Oretha Castle Haley Boulevard. A second show is planned for Saturday.

During his talk, Raeburn noted that many believe Morton’s name change was a strategic choice that would serve the Creole musician and former Indian “spy boy” better for a career in American popular music at the turn of the 20th century. But it was his very Creoleness, the multiplicity of influences that he distilled into his sound, Raeburn said later, that made his work so compelling.

“No one was as eclectic in the jazz context,” Raeburn said. “The fact that he drew so broadly and was aware of what he was doing. He talks about mixing the ‘Spanish tinge’ with the blues — the Afrocentric, Cuban, Haitian — he was swimming in all that, reflecting the diversity that was present in his environment.”

The “Jelly Roll Blues,” for example, is “a rag that swings” but also hints at an Argentine tango and at a new sound entirely, one guest pointed out.

Widely acknowledged as the first published jazz composition, “Jelly Roll Blues,” released in 1915, may also have been the subject of one of the first musical shout-outs: “The Darktown Strutters’ Ball,” published two years later, namechecks the tune in its lyrics.

Living in the U.S. after the Supreme Court’s landmark 1896 decision in favor of racial segregation, Plessy v. Ferguson, Raeburn said, a Creole person was in a unique position, “living in both worlds.”

“And both worlds are what you need when you want to cover the whole New Orleans trick bag,” he said.

In that, Morton wasn’t only the first great American jazz composer — he was the first genuinely New Orleanian jazz composer.

That is demonstrated in the 1938 audio recording, as Morton describes the movements of a Mardi Gras Indians dance. While doing so, the pianist taps out a rattling rhythm while launching into “Hu-ta-nay, two-way-pocky-way,” a chant Indians still sing today.