Confound it -- what IS Gnarls?

They’re a hip-hop Mutt and Jeff: one tall and lanky with a kinky red Afro and a tendency to devote earnest thought to even the most lighthearted matters; the other a short, bald, rotund guy who peppers his conversation with arcane mythological and spiritual references.

But already the musicians collaborating under the jokey name Gnarls Barkley -- Grammy-nominated producer Danger Mouse and soul dynamo Cee-Lo Green -- are being eyeballed as one of the year’s most intriguing new arrivals.

Neither is a household name, but their musical bona fides are impeccable. In 2004, Danger Mouse (real name: Brian Burton) created a “mash-up” of the Beatles’ so-called White Album and rapper Jay-Z’s “The Black Album.” Calling it “The Grey Album,” that marriage of disparate genres became a watershed event in hip-hop. As a result, Burton was tapped to produce the conceptual rock-dub band Gorillaz’s second album, “Demon Days,” for which he received a Grammy nomination.

Green -- real name Thomas DeCarlo Callaway -- was a high school classmate of OutKast’s Andre 3000 and Big Boi, and his vocal approach is credited with precipitating Andre 3000’s shift away from rapping to take hip-hop in a new direction with his own singing.

Gnarls Barkley’s infectious lead single “Crazy” -- on which Cee-Lo channels Al Green’s falsetto and Sam Cooke’s pitch control atop an analog hip-hop groove -- stormed Britain this week, coming in at No. 1 at the Apple iTunes UK Music Store.

Even with the release of their highly anticipated debut album, “St. Elsewhere,” still seven weeks away, they have not only confounded music critics trying to classify their alterna-hip-hop sound, they have confounded themselves.

So Burton and Callaway agree to disagree about where their music fits. “It’s so cliche to say that it’s not classifiable or ‘It’s like nothing else,’ ” said Los Angeles native Burton. “I think it’s more of a rock record but with hip-hop’s underlying spirit. An alternative to R&B.;”

“It’s funk,” said Callaway, a founding member of the Atlanta rap quartet Goodie Mob. “A lot of my music is centered in a place where I want to be pleasing in the sight of my maker. But it’s not formal gospel. Gospel is at funk’s center. And it’s vintage soul because I’m an old soul.”

They are hardly alone in their inability to categorize Gnarls’ singular blend of styles. It mines -- but isn’t limited to -- ‘60s psychedelia, throbbing Miami-bass, Motown music, trip-hop and hot buttered soul; the record Marvin Gaye might have made he had come of age in an era of digital samplers.

At least six of “St. Elsewhere’s” tracks hit file-sharing websites four months ago and have gone on to become the passion of music bloggers.

Gnarls Barkley is slated for a prestigious public debut May 1 at the Coachella Valley Music & Arts Festival, and the duo has been added to Lollapalooza 2006 in Chicago in August.

The two came together to record a remix for Burton’s “Ghetto Pop Life” album but began collaborating as a kind of proto-Gnarls in mid-2003. They recorded batches of songs at Callaway’s Atlanta studio even though the prospect of a record deal was far off.

“We took an independent approach, funding the sessions out of our own pockets,” said Callaway, seated in the lobby of Santa Monica’s Viceroy Hotel. “This album has no predecessor; there’s nothing to ensure it’s going to work in any genre or market. But we weren’t taking ourselves too seriously. It’s a very organic, honest record.”

When their schedules prevented them from getting together, the band mates worked separately, then e-mailed each other. The absence of physical proximity often resulted in some outre lyrical content. Callaway sings about necrophilia, feng shui, the TV cartoon “Transformers” and he even apes the Violent Femmes’ angst-art-rock classic, “Gone Daddy Gone.”

“Impressed as I was with [Burton’s] production and ideas for the record, I wanted to shock and surprise him as well,” Callaway said. They eventually signed with Downtown/Atlantic Records and have already begun work on a second Gnarls album.

“I want to get another record done, hopefully before this one gets too big,” Burton said. “I don’t want to worry about what the public will want to hear next.”

As for the group’s name -- a hip-hop-ization of former NBA star Charles Barkley -- suffice to say it’s equal parts declaration of purpose and goofy humor.

“We were looking for a name that sounds like its own genre,” Burton said, seated near a mixing board at a Burbank recording studio where he was producing tracks for New York dancerock group the Rapture. “A perfect example is when I heard of [electronica musician] Aphex Twin. It could describe a sound. And there was just something familiar about Gnarls Barkley.”