The pop musician Will.i.am is anything but quiet. When you hear his name or see his face, it may be difficult to think of anything but a metallic voice chanting, “Let the beat raaaahck.”

But Will.i.am (real name: William Adams) has amounted to a quiet equity partner in Beats Electronics, the company known for its fashionable Beats by Dr. Dre headphones and its newer Beats Music streaming service. Yes, he has loudly shown his support for the product by plugging it in songs and music videos again and again — but the fact that Adams has an ownership stake in Beats has been rarely reported, even though his role is clearly indicated on his personal website.

For the last few years, Adams has been trying to fashion himself into a businessman, with particular focus on the technology industry. (See Fortune‘s profile of him in the 2013 Future Issue: “Corporate America’s hit machine.”) “Trying” being the operative word: Last year, his hardware company i.am+ released its first product, a digital camera accessory for iPhone called the i.am+ foto sosho, a $325 snap-on lens for the iPhone; it flopped. Last month, he announced on television his next product, a forthcoming smartwatch; it was met with some ridicule in the tech press.

And then there’s Dipdive, a multimedia lifestyle website Adams created a few years back after meeting Napster co-founder Shawn Fanning. “He told me, ‘you should understand this world.’ And that’s what got me tech savvy,” Adams told Fortune in an interview last year. Adams said Fanning advised him to approach his record company and try to get ownership over the blackeyedpeas.com domain name. He did, and subsequently approached Interscope chairman Jimmy Iovine — the Beats co-founder — asking to take over interscope.com so he could turn it into a more social site. The label declined, but Adams’s idea became Dipdive, which he intended as a Myspace-like community that would connect musicians with big brands.

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“Success,” Adams said, “looks like this: You’re so big that brands want to partner with you. But now, what company provides that? That doesn’t exist! Who gets you in touch with a brand?” It was a nice idea, but it eventually deteriorated into a dumping ground for Black Eyed Peas videos. (Today, it simply redirects to the official Will.i.am site.) When asked what happened to it, Adams shrugged and said, “Ehh, I don’t want to do it anymore. I have something else I’m doing.” Adams insisted Dipdive wasn’t a failure, because the backing code and social technology he learned for the project would serve him in the future.

Adams declined to comment for this story, and has yet to speak publicly about the rumored Apple-Beats deal. But it’s safe to say that if the acquisition is indeed real, Beats is far and away the most successful business venture in which Adams has been involved. Though his name is not on the product — that would be Dr. Dre, the stage name of rapper and mega-producer Andre Young — he is the company’s third equity partner alongside Iovine and Young. His ownership percentage is not known, but in February he told the crowd at Midem 2014, a music-industry trade show in France, that he has made more money from his equity stake in Beats than he ever did from the record-breaking, Grammy Award-winning 2009 single, “I Gotta Feeling.”

The name on the headphones may say “Dr. Dre,” but Adams has certainly pulled his weight as a partner by marketing the hell out of the brand. At the 2011 Super Bowl, the Black Eyed Peas performed on a stage that was shaped like the Beats logo, a lowercase “B.” (Some reports said that Adams fooled the NFL into shaping the stage that way.) He has worked the product into countless hit songs and videos, either visually or with a shout-out (“I be rockin’ them Beats!” he yells in the U.S. chart-topping 2009 single “Boom Boom Pow”; the video for his 2012 single “Scream and Shout” with Britney Spears, another chart-topper, is laced with promotional shots of the Pill, a Beats portable speaker).

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Over the last few years, Beats has experienced several ownership changes. In August 2011, the Taiwanese smartphone manufacturer HTC purchased a majority stake in Beats for a reported $300 million, but in July 2012 Beats paid $150 million to buy back 25% of HTC’s stake. (Adams told Fortune that he used a portion of his proceeds from that deal as seed capital for the i.am+ camera.) In September 2013, HTC sold back the rest of its stake for $265 million, a modest gain on its original investment. At the same time, Carlyle Group invested $500 million in the company. Four months later, the company launched Beats Music.

Adams said that from the very beginning, Iovine and Young approached him and asked if he’d want be involved in a headphones company. (Iovine also declined to comment for this story.) Adams recalled the conversation. He asked, “Headphones? It was supposed to be hardware and computers.” Their response: “Yeah, but how do you think we’re going to get there? We’re going to have Dr. Dre headphones, and eventually we do Will.i.am or Black Eyed Pea headphones.” Adams had no interest in headphones branded with his name, but agreed to take on a quiet part-ownership role. “I’ll still market it, I’ll still put my head on it,” he told the pair. “But I want to eventually do hardware, with software connected to it. So I don’t want anything to take me away from that.” (Beats eventually went on to sell “Heartbeats” earphones with Lady Gaga and “Diddybeats” earphones with Sean “Diddy” Combs, among others; those models have been discontinued.)

In fact, the Beats logo is identical to the ‘b’ from the original Black Eyed Peas logo, last used in 1998. “I don’t think the public even knows everything he’s behind,” former Interscope president Steve Stoute told Fortune. Adams told Fortune that he had been eyeing hardware since 2003, when he first noticed people were watching entire concerts on their phones; he told Iovine that they needed to team up to make hardware, and recalled that Iovine responded, “Will, do you know how hard that is? That’s why they call it hardware.”

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It’s clear that Adams understands the marketing power of a musician’s name. Asked about the “Beats by Dr. Dre” name last year, he told Fortune, “They turned him into a brand of consumer electronic goods because he’s synonymous with sound. That’s pretty brilliant.” The failure of Adams’s camera may have been an indication that the Will.i.am name is not as strong with consumers as that of Dr. Dre, at least as it pertains to studio-quality sound. But Beats “is all the proof that I need that my mind and thinking around consumer products can be effective,” Adams said. “In 2005 when you walked down the airport you didn’t see headphone stores. Now there’s headphone stores in every airport on the planet. And Beats played a big role in that. The consulting of Beats and the direction we took, I played a role in that.”

And it’s worth noting that Apple helped the Black Eyed Peas when it featured their song “Hey Mama” in its very first iTunes + iPod commercial. Last year, Adams told Fortune that there were talks with the company about the possibility of a “Black Eyed Pod,” à la the U2-branded iPod that Apple released in 2004.

Ken Hertz, an entertainment lawyer who has worked with the Black Eyed Peas for years, said, “Will is the best marketing partner a brand could ever ask for. He moves quickly, thinks on his feet, and he loves the art and science of it. He has an innate understanding for what consumers will actually enjoy from brands.”

For Beats, Adams “chose not to be the face of the company,” Hertz said. For that reason, Beats.i.am was never in the cards. Not that Adams minds.