At this spring's TV upfronts, the annual gathering in New York where networks attempt to woo and wow advertisers with sneak peeks of their upcoming season of programming, the most sensational development wasn't the unveiling of a new musical or blockbuster sci-fi series-but the arrival, on a drizzly evening, of Jay-Z.

The global rap star put on a memorable, hourlong performance as the special guest of Adult Swim-the Cartoon Network's nightly oddball animation and comedy block that Nielsen consistently rates No. 1 on cable among 18- to 49-year-olds. If Jay-Z and Adult Swim seem like an odd pairing, it won't for long: The network, which has owned and operated its own record label since 2007, is leaving an increasingly conspicuous footprint on the music industry.

Ano indentt first glance, Williams Street Records is diminutive. The label, housed in the shadow of the Turner Network campus in Atlanta, at Williams Street Studios-the Cartoon Network-owned production company behind Adult Swim-has all of three official employees, each of whom has day jobs working in other capacities on what they call "the kids side." But such balancing of disciplines among a tiny, impassioned staff is indicative of the collaborative, open-door ethos to which the label owes both its success and existence.

In 2004, Jason DeMarco was working as associate creative director for a Cartoon Network afternoon showcase called Toonami, for which he was responsible for writing promos and finding music to play alongside action-packed cartoons for adolescents. One of the producers he worked with to provide original music was a local artist going by the name of DJ Danger Mouse. Before he went on to become a Grammy Award-winning super-producer and one-half of hitmaking act Gnarls Barkley, Danger Mouse was riding high thanks to buzz from an illegal but influential bootleg of mashed-up Jay-Z and Beatles songs that he made called The Grey Album. The producer came to DeMarco with the idea of doing a different kind of mashup project-this time pitting the vocals of Toonami characters against underground hip-hop hero MF Doom over his own production. DeMarco liked the idea, but knew there was a better option.

"Why don't we take it over to Adult Swim?" he suggested.

Brass at the late-night programming block, then in its third year, were already big fans of left-field hip-hop, having frequently used beats from artists like J Dilla and Madlib to soundtrack their signature "bumps" between commercial breaks. Mike Lazzo, head of Williams Street Studios, agreed to contribute funding to the project, which became known as Danger Doom: The Mouse and the Mask, and was released in 2005 on Epitaph. The album featured guest appearances by characters from popular Adult Swim shows like "Aqua Teen Hunger Force" and "Space Ghost Coast to Coast," and was promoted heavily in the network's bumps. On release, it debuted at No. 2 on Billboard's independent albums chart and received largely positive reviews from critics. DeMarco and Lazzo began to think they were onto something.

"After Danger Doom, we started to have the conversation," DeMarco recalls. "'If we can put out records for other companies, could we possibly do it ourselves?'"

The answer, it turned out, was "yes." Considering its size and background, Williams Street Records, which is distributed through Warner Music's Alternative Distribution Alliance, has been surprisingly prolific. Since 2006, the label has released or co-released more than 18 albums. The gamut of projects is defiantly varied, ranging from compilations with grime rap, Afropop or metal themes to studio albums by Dungeon Family artist Witchdoctor, New York hard rock band Cheeseburger and, most recently, the youthful punks of Cerebral Ballzy. The compilations are available for free on the Adult Swim website, while the studio albums are sold for $12 through the Adult Swim online store, iTunes and other retailers. Perhaps the only obvious link between the albums that Williams Street releases is the pervasive sense that at any other label, they wouldn't, or couldn't, have existed.

"If we come across an artist or band we admire that is unsigned, we all sort of put our heads together and decide if it's something we feel like we can support on air and out in the world," says Amantha Walden, the former owner of Atlanta-based indie Velocette Records who was brought in to head up Williams Street Records in 2007 and also serves as Cartoon Network's top music supervisor. "Because we have a TV network at our disposal, we can do certain things that maybe other indie labels can't, like air a 30-second spot five nights a week, or a music video, or some other short-form content. That hybrid has been amazing for us."

As with Adult Swim, Williams Street Records appeals to a core demographic of 18-34 males and gains traction in part by marketing directly to college campuses. The label puts on an annual tour of free college shows, the Ragbag of Jollification tour, which this year hit 10 towns from College Station, Texas, to East Lansing, Mich., and featured performances by Wavves, How to Dress Well, Pusha T and others. While Williams Street won't disclose its annual budget ("low," Walden says), sources describe both the shows and the free albums as calculated expenses designed to increase brand loyalty to its corporate parents.

"This is all sort of experimental for our company," says DeMarco, now head of A&R for Williams Street Records and creative director of sales promotions at Cartoon Network. "As a source of income, we're a drop in the bucket compared with TV revenues, so for us it's more important to get things right as opposed to keeping to a schedule of x number of releases."

To date, Williams Street's best-selling artist is a talent that came from right under its nose.

The hit Adult Swim show "Metalocalypse," co-created by lifelong death metal fan and erstwhile musician Brendon Small, was almost tailor-made for a Williams Street crossover. Its stars are the brutal, and fictional, death metal band Dethklok, who perform original music in every episode that Small composes and performs himself. In 2007, Williams Street put out a proper Dethklok album, The Dethalbum, which, thanks in large part to the show's rabid fan base, became the fastest-selling death metal album in history, moving 34,000 first-week units, according to Nielsen SoundScan, and debuting at No. 21 on the Billboard 200. The label sent Small and a backing band on a 28-city tour that sold out midsize venues across the country. A sequel, 2009's Metalocalypse: Dethalbum II, did even better, bowing at No. 15 on the Billboard 200 with 45,000 units. All told, Dethklok has sold 522,000 albums.

When Williams Street isn't making musicians out of Adult Swim stars, it's making Adult Swim stars out of musicians. Cerebral Ballzy, a hardcore punk band with a cult following from East New York, was courted by Walden as a fresh act that could possibly grow with the label during a multi-album deal. For the band's self-titled debut, released in late July, Williams Street shot music videos for nearly every song and put some in rotation on the network. The reaction from fans has been perhaps more positive than even the label imagined.

"Our audience has really responded well to it. And that is not a given, because the Adult Swim viewer is very opinionated," Walden says. "But I think Cerebral Ballzy has the same spirit Adult Swim has, which is sort of anti-authority and independent." Adult Swim's reputation as an authentic and youth-approved institution has enabled Williams Street to pursue collaborations with some of music's most sought-after acts. The company's Singles Program, which recently completed its second summer, is an annual series of free, unreleased MP3s from of-the-moment acts like Best Coast, Washed Out, Black Lips and JJ. Last year, the program released eight singles in eight weeks; this year it was 10 in 10.

"I literally make a list of all the artists I'm listening to and just start making phone calls," says DeMarco, who can't remember being rejected due to his affiliation with cartoon programming. "You talk to pretty much any musician in the U.S. and they love Adult Swim, because they came home late from a gig one night, and at 4 a.m. 'Aqua Teen Hunger Force' was on."

Rather than dealing with signing artists to a one-song deal, or facing roadblocks from working with certain acts because of pre-existing contracts, the Singles Program is done as a promotional series made possible by a corporate sponsorship with auto manufacturer Kia.

"Appealing to the youth market is important to us," says Tim Chaney, director of marketing communications for Kia Motors America, which uses the Singles Program to promote its youth-oriented Soul SUV. "Partnering with a top cable network is the perfect way to reach our target audience."

The funding from the partnership allows Williams Street to step in and take care of the logistics of realizing the songs where necessary, whether that means paying for studio time, mastering the recording or anything in between.

"Whatever we need to do to help them get it done, we do," DeMarco says. "Each year it almost breaks me, but it's totally worth it." Chaney says that Kia, for its part, is "pleased with the results."

Deno indentMarco's biggest challenge by far was the Jay-Z booking. It started last year, when Lazzo and Adult Swim VP of program development Nick Weidenfeld asked him to pull out all the stops for their next upfront showcase. In 2008 Kanye West performed; in 2010, M.I.A. "They said they wanted someone really, really big-Jay-Z level," DeMarco says. "I said, 'Well, we'll never get Jay-Z, so forget about it.' But they told me, 'You have to try.'"

DeMarco had a contact with Jay-Z's business partner/manager John Meneilly, and reached out to him to discuss a possible appearance from the superstar, who at the time had 11 No. 1 albums to his credit (now 12). All in all, he says negotiations took "about a year."

"Jay was interested in a deeper relationship than just playing a show," he says. Speculation has circled that the serial entrepreneur was after a development deal with the network, but DeMarco won't confirm precisely what the two parties are up to. Whatever terms were reached, the negotiations were clearly a success. The superstar's packed set at New York's Roseland Ballroom was sprinkled with knowing Adult Swim references. "He has to finish his Watch the Throne stuff, but hopefully we'll be doing more with Jay soon," DeMarco says.

For the near future, Adult Swim already has a pair of other high-profile music collaborations up its sleeve. The network has ordered TV pilots from rising firebrands Odd Future and Diplo's globe-trotting, neo-dancehall act Major Lazer. At Williams Street Records, DeMarco is readying a new compilation of unreleased music from U.K. dubstep and electronic artists called Unclassified, which will feature songs by Burial, Actress, Kode9, Skream and others. The project will be released for free in September thanks to a partnership with car marque Scion.

Next year, along with new albums from Cerebral Ballzy and Dethklok, the label plans to put out a full-length record from Atlanta-based underground hip-hop hero and former OutKast affiliate Mike Bigga (formerly known as Killer Mike). The album, titled R.A.P. Music, is being produced entirely by El-P, a former member of influential '90s rap group Company Flow. The veteran producer/MC is also the founder of iconic independent hip-hop label Definitive Jux, which collaborated with Williams Street on one of its first compilations, Definitive Swim.

"Musicians love what Adult Swim does," El-P says, recalling his experiences working with the company. "They kind of just let us do whatever the fuck we wanted to do."••••

Reggie Ugwu (@ocugwu) writes for Complex and Billboard magazines, among other publications.