He scored his first global hit, Where is the Love, with the Peas and Justin Timberlake in 2003 and his latest, Scream & Shout, featuring Britney Spears, last November. In between, he has had dozens of hits, solo, with the Peas and as a featured artist, and quite a number of flops too, none of which seem to have dented his impermeable self-confidence.
With his bright, loud, colourful, plastic sounds and restless ever-shifting productions mixing sing-song melodies, rap and dance beats, will.i.am is one of the people who has most shaped the sound of popular music right now, for better or worse.
He has released three solo albums, six Black Eyed Peas albums and collaborated with an astonishing who's who of modern music, including Michael Jackson, U2, Rihanna, Mick Jagger, Pussycat Dolls, Mary J. Blige, Cheryl Cole and Earth, Wind and Fire. His next single, #thatPower - he has become fond of "hashtagging" titles, to make them Twitter-ready - features Justin Bieber, the Canadian heart-throb lending teen appeal to a squelchy club number.
"Justin's going to be okay," Adams says of the 19-year-old star's recent bad press for tardiness and petulance. "It's dangerous to be a child star, but it's dangerous to be a child in the ghetto, or to be a child at school being bullied. "If you have good parents, you'll be all right. Justin's mum is great."
Adams says his own mother gave him "encouragement, attention, discipline". He was born in Los Angeles in 1975, and raised in the housing projects in the east of the city. He never knew his father but his mother discouraged involvement in gang culture and nurtured his creativity and self-confidence. "My mum did a good job," he says.
He comes across as quite an odd character. Always immaculately groomed, he appears today in black jeans, a sleek, pale pink jacket and gold patterned trainers.
He's sporting a short, asymmetrical haircut, graphic designer glasses and neat facial hair. He rarely answers questions in a straightforward way, often diverting them into a kind of interrogatory mode, where he stages both sides of the conversation. This tic could come across as hectoring and sarcastic but he's got such a gentle manner and a genuine, boyish smile that there seems to be no malice intended.
Still, in some ways, he makes me feel extraneous to the conversation. He has the strangeness of someone who's been famous too long, constantly surrounded by people telling him how wonderful he is and serving his every need. One of his retinue is in the room throughout our interview and Adams often seems to be pitching his remarks towards her.
As will.i.am, Adams has a new album out at the end of the month, #willpower, which he describes as a "genre fusion", meshing "big orchestra, laptop computer music and sonics for the dance floor".
We'll have to take his word for it, though, because he won't let anyone hear it while "there's still last-minute tweaks to make everything sound right". He has the only copy and is paranoid about internet leaks, which have beset the album throughout the recording process. "I wish it didn't have to be that way," he says.
He has been in Prague recording with an 80-piece orchestra. "I'm creating drama, drones, cinematic endings and beginnings. I know people are going to hear my songs on YouTube, where they have to compete with movies, libraries, conspiracies, government files, this sea of humanity's history.
"So when my music comes on, how are they gonna know it's my song? Is there some way that each one of my songs starts and ends so that there's tentacles that reach out and grab towards you? I think of all that now. I think of the visual component - what's the logo? What's the colour palette? If the song was a brand bible, what would it say?"
The 38-year-old, who is currently embroiled in a copyright dispute after Russian D.J. Arty accused him of stealing the beat for his Chris Brown collaboration Let's Go, suspects pop is getting ready for a sea change. "So I go out and search, go to the underground and see what people can adopt on the surface". He talks about "song-documentaries", citing his (as yet unrevealed) album tracks Ghetto Ghetto and The World's Going Crazy.
"It's a new genre. Imagine Bob Marley if he wrote Get Up, Stand Up in the days of the internet and showed you all the injustices in the world. Rebellious, uplifting, motivational music with imagery and facts attached. You can do that now. I have a whole bunch of content for how connected we are today."
A self-proclaimed technology geek, Adams has a role as creative consultant with computer corporation Intel, collaborates with Coca-Cola on an inventive environmental initiative, Ekocycle, and is a major equity partner in Beats Electronics, which developed Dr Dre's best-selling range of designer headphones.
A gold-trimmed camera hangs around his neck, the iam+ fotosho, his own-design snap-on iPhone accessory that dramatically improves the phone's photo capabilities.
He's also got a philanthropical bent - last year, he donated half a million pounds to The Prince's Trust to fund education, training and enterprise schemes with a focus on technology. "The world doesn't need another songwriter or singer," he says. "Are we preparing our kids to be the leaders of the world? Hey, 11-or-12-year-old, you should probably want to be a scientist, a technician, coder, engineer or mathematician. That's what I believe and I put my money where my vision is."
Yet he is also a judge on Britain's The Voice, another music reality show producing wave after wave of wannabe pop stars. He talks himself into knots defending the programme. He is touchy about the failure of the first series to produce a bona fide star, apportioning blame on everything but the programme itself.
I point out he himself wouldn't have made it through the first auditions, since he has to rely heavily on Autotune to correct his flat vocals. "No, no, no, no, that's like a saxophone telling a piano it is not a wind instrument," he protests, apparently offended. I am not entirely sure what he means, but his point seems to be that The Voice "is good for wind instruments" (i.e. singing) whereas he has a different skill set. "What Autotune allows is for people like myself and Kanye West not to depend on the singer.
Back in the 50s, the songwriter was rendered invisible. Now the songwriter is there in the forefront."
This leads to an amusing, affectionate digression about working with Michael Jackson on a number of tracks which, following Jackson's death in 2009, he eventually decided not to release. Jackson apparently wanted Adams to apply Autotune technology to his voice: "He said, 'I just love that sound'," recalls Adams.
But it didn't work because "that plug-in is looking for imperfections and, as soon as something goes slightly off, it pulls it back to where it should be. Michael had perfect pitch, so the machine had nothing to do. I told him he had to sing out of key on purpose. He said, 'I can't do that!"'
Adams claims to suffer from "ADD" (Attention Deficit Disorder), though I never get to the bottom of whether this is a medical judgment or a self-diagnosis. I'm not sure he even knows what ADD is, at one point saying "it's not a disability, it's an amplification because you are able to pay attention to a lot of different things at once, while giving full dedication to one thing".
He immediately contradicts himself by saying "my attention span is very short. That's good [for songwriting]. Anything can distract me, so if it sticks in my head, it'll stick in other people's heads." In any case, it seems an approach to life that is entirely in keeping with what he defines as the "hyper-inflated, connected world we live in, where everything is now, now, now - which is a gift and a curse".
Adams is a fascinating man, smart, mercurial, hugely talented but more than a little self-obsessed. He becomes animated when we get into a discussion of the 2004 Black Eyed Peas song Let's Get It Started, a key single in what is known in the recording world as the Loudness War, when (as Greg Milner explains in his fascinating book Perfecting Sound Forever: The Story Of Recorded Music) tracks were being compressed and boosted so that they sound loud even when volume control is set low.
American mastering engineer Bob Katz described Let's Get It Started as "one of the worst-sounding, most distorted, over-compressed pop records ever made". It was also a global hit, which forced everyone else to adopt the same techniques to compete, and heralded a modern pop era of everything firing on all cylinders at the same time.
Without getting too technical, if you viewed the track as a visual diagram, the sound waves peak beyond the recording spectrum, so they have to be constantly clipped, ending up in a geometric shape like a solid wall rather than a curve of peaks and troughs.
Adams launches into a description of how, if you play it on modern club speakers, you get the complete sound wave. I have the feeling he is talking complete rot but there is no contradicting him. Then he sets off on a tangent about new developments in speaker technology, where "they don't just move air, they move matter! You're gonna start seeing different types of equipment, how you feel music, not just sub-frequencies but even down to the neurological level."
There's a dreamy look in his eye, like he is imagining the possibilities for his next hit.
• will.i.am performs at Hallenstein Brothers' Ultimate After Party in Auckland on Wednesday. #thatPower and #willpower are out now.
