In a career spanning more than half a century, Dr. John’s name has been synonymous with the music of New Orleans. Once very plausibly described as “the blackest white man in the world,” he has indefatigably upheld — and updated — the various sounds he heard while growing up amid that city’s vibrant African-American culture.

Dr. John has been honored with a Grammy in both the jazz and blues fields. His first records in the late 1960s, meanwhile, were inspired by local voodoo music, but fortuitously chimed with hippie rock. The man himself prefers to be filed more loosely: Having long since adopted the jive parlance of his heroes, he describes himself as, simply, “fonky.”

Among other musicians, Dr. John, whose real name Mac Rebennack, commands almost unrivaled respect. By no small coincidence, three tracks from his new album include guest contributions from Eric Clapton, a long-standing admirer.

Titled “City That Care Forgot,” this record finds Mr. Rebennack at the very top of his game, as he seeks to express the anger, paranoia, and despair still rife among New Orleans’s scattered former inhabitants, in the wake of Hurricane Katrina. The bonus attraction of Mr. Clapton’s inimitably fluid guitar-playing means, inevitably, that more people will get to hear Rebennack’s wake-up call.

The two first met in 1969 in Los Angeles, where Mr. Rebennack was living at the time, and where Mr. Clapton had just landed, after quitting Blind Faith. A few months later, Mr. Rebennack set up some sessions in London for a putative triple concept album, to be called “The Sun, Moon & Herbs.” Mr. Clapton was the first to arrive, followed by Mick Jagger and 30-odd percussionists of varying Afro-Caribbean origin. The release was ultimately trimmed down to a single album.

“We’ve had all kinds of weird hookups at different times,” Mr. Rebennack said, when I met him in New York. “About the third time I met Eric, he was upset because I said that song [hums the riff to Cream’s “Sunshine of Your Love”] was by Jimi Hendrix. The fact is, I wasn’t the most connected-to-the-planet guy at that time, and me and Hendrix had been doing gigs together. I didn’t mean to upset him.

“We eventually got past that. I knew all the guys from Cream, but Eric was the one who always seemed to be around.”

Rather like Woody Allen’s ubiquitous character, Zelig, Mr. Rebennack himself has “always seemed to be around,” among rock’s top brass. He was in the room, for instance, when Little Richard cut “Tutti Frutti.” He has himself recorded with John Lennon, the Rolling Stones, and Van Morrison, among innumerable others. Perhaps coolest of all, his biggest hit, “Right Place, Wrong Time,” featured the line, “I’m on the right trip, but I’m in the wrong car” — written for him by Bob Dylan.

Before all that, he earned his stripes as New Orleans’s cultural ambassador. Mr. Rebennack was hanging out on the predominantly black R&B scene by the age of 12. He received guitar lessons from some of its prime movers, and also collected drugs for other less salubrious characters. Within a couple of years, he was a heroin addict, gigging and recording with his mentors as an equal.

In a brawl in the early ’60s, he shot off the ring finger of his left hand — not a happy occurrence for a guitarist — and was forced to switch to piano. After dabbling in pimping to fund his drug habit, he eventually wound up in prison. On his release, a campaign was under way to clean up New Orleans by closing its clubs, which meant that he and his buddies were driven away to find work. Thus he wound up in California in time for flower power.

If his subsequent career — mostly conducted in exile — has been about salvaging New Orleans R&B and other traditions from extinction, it has acquired a renewed sense of urgency, post-Katrina. “City That Care Forgot” is all about re-establishing his hometown’s recovery on the political agenda.

“I couldn’t live with myself if I didn’t do this record,” he said. “It ain’t like musicians know anything more than anybody else. I’m just trying to be a voice for people that ain’t got none right now.”

For two hours, Mr. Rebennack, now 67, vents his anger about all the human tragedy, and the shady maneuvering, which, he believes, lies behind the government’s mishandling of the disaster.

He explains how the songs “Land Grab” and “Black Gold” are about the eradication of swampland to allow for oil drilling, thus destroying an ecological buffer against hurricane damage. Other tracks lay the blame at the door of the White House.

Though the album has its spooky moments, it is musically upbeat, even jubilant. It is also about throwing a lifeline to New Orleans’s music scene.

“I’m just lucky still to be getting a gig,” he said. “It isn’t like I’m living in the style of the rich and wealthy here, so anything that’s rolling is good. I was homeless before it became fashionable. But at least I remember where I came from.”

He smiled, finally. “A lot of stuff I forgot, but that much I remember.”