He invented funk, defined the sound of New Orleans, and crafted #1 records for countless artists. But his favorite creation was a song almost nobody heard.

Allen Toussaint’s final album, American Tunes, is an elegant farewell that spotlights his under-appreciated gifts as a pianist and interpreter, but to understand Toussaint’s true genius, you have to hear his legendary work as a writer, arranger, and producer. Where to start? Take your pick: The Wild Tchoupatoulas album he produced nearly defines the sound of New Orleans and gave birth to the Neville Brothers. The series of records he made with The Meters pretty much invented funk music. His own run of solo albums in the ’70s are quiet masterpieces of grace and groove that continue to grow in stature. And then there are the songs he wrote and/or produced for others that became #1 records across pretty much every chart Billboard could put a name to, including R&B, Country, Easy Listening, Adult Contemporary, and Pop. He’s collaborated with The Band, Paul McCartney and Elvis Costello and his songs have covered by everyone from The Rolling Stones to Glen Campbell, Paul Weller to Phish.

His deep humility and comfort behind the scenes are the only reasons he isn’t a household name, but it’s a safe bet that every household has been warmed by a record Toussaint wrote, produced, contributed to or was sampled on. His influence and impact on music is simply immeasurable. And there’s really no point of diminishing returns with his music, either — you can put on nearly any record he’s touched and it will be at least great. I made a habit long ago of buying any album he produced and I’ve been rewarded dozens of times (the unfathomably soulful High Life album introduced me to the great Frankie Miller) and disappointed exactly once (sorry, but it’s a violation of Trunkworthy’s mission to call that one out by name).

“If I was to think of a song that I think the most of in my life, it wasn’t heard by anyone but me and the artist, Lou Johnson; a song called “Transition.”

But the song Allen Toussaint himself would likely want you to listen to and hold up as his greatest moment is one that sounds at once like nothing and everything you’d ever expect from him. It’s the song that that Toussaint repeatedly called out as his favorite, and the one he wished more people had the chance to hear. It’s called “Transition” and it’s an 8-minute, psychedelic prog-soul opera unlike anything he’d done before or since and certainly unlike anything you’ll ever experience. It was a song so close to Toussaint’s heart that he continued to talk it up, unprompted, in interviews decades after it had fallen out of print. He mentioned “Transition” to Uncut last year saying“if I was to grade myself on how you did as a songwriter, I would probably put that down.” Then just last March he called “Transition” out again when Offbeat asked his personal favorite of the songs he’d written, lamenting, “No one knows it but me . . . it’s long lost.”

It could only be the work of a master at the peak of his powers, playing in the sandbox of his own genius.

Originally released in 1971 on the mighty Stax/Volt label, “Transition” was the centerpiece of With You In Mind by Lou Johnson, a powerhouse R&B singer who’s claim to record-collector fame is rooted in cutting the original 1963 version of Naked Eyes’ synth-pop hit “Always Something There To Remind Me.” Too long to fit on a 45, defiantly avant-garde by any standard, and buried in a barely-heard album by a barely known singer, the obscurity of “Transition” was guaranteed from day one despite the place it held in Toussaint’s heart. Equal parts Sgt. Pepper, Superfly, and Brian Wilson’s Smile, with about a dozen other genres doing battle in between, “Transition” follows a man falling in love, losing love, begging for it back and descending in to madness in the process. The song is broken up in movements, beginning with something close to a Broadway show tune and closing with something that sounds like John Coltrane and György Ligeti leading an orchestra in revolt against music itself, reducing Johnson to howling and screaming nonsense in the process. It’s at times funny, gorgeous, funky, and downright terrifying. It’s an epic listen . . . and could only be the work of a master at the peak of his powers, playing in the sandbox of his own genius.

Allen Toussaint will always be associated with funk, R&B, jazz, and the music of New Orleans, but “Transition” is the song that shows virtually everything he was capable of. It’s no surprise or great injustice that this wasn’t a hit, but when a genius with a resumé as deep and monumental as Allen Toussaint points out a song as his proudest moment, it damn well deserves a listen. And we think it rewards it, too.

BONUS CUT: Since “Transition” is admittedly a bold departure from (or bold synthesis of) Allen Toussaint’s typical output, we put together a few of the more emblematic tracks he wrote and/or produced for himself and others.