Birthdays come and go, but the big 4-0 is a pretty good occasion to stop, take stock, and think about how far you've come. That's true even for kimono-loving, skin-care-enthusiast, white-tee-obsessive, DIY-specialist John Mayer, who turns 40 on October 16. He just does the taking-stock thing a little bit more extravagantly than the rest of us.

To mark the occasion, Mayer commissioned a particularly ridiculous piece from L.A.-based jeweler to the stars Ben Baller of If & Co. Now, Mayer is no stranger to a lavish jewelry purchase—he's got Patek Philippe watches worth more than most cars—but this time around he really outdid himself. How? We're talking about a necklace featuring the diamond-encrusted head of The Dude from The Big Lebowski. For a piece this special and this insane, we had to hear the backstory, so we asked Ben to explain how this ostentatious and, to be honest, pretty amazing piece of neckwear came to be.

GQ: When did you first start working with John Mayer?

Ben Baller: We have one mutual friend who's a client of mine. It’s a pretty tight community in streetwear—not urban streetwear, but like Japanese high-end. John’s always been really fond of, like, Visvim, Acronym, super high-end, exclusive brands.

I never know who’s going to call me, you know what I mean? I used to do Michael Jackson’s jewelry. I’ve done crazy people’s jewelry. Me and John struck it on a whole different level; we really hit it off. But we met two years ago. I can’t remember the first piece—I’ve made him a lot of pieces, but it’s stuff that I can’t really talk about. For his privacy. But I’ve made him a lot of pieces.

So did he tell you, "Hey, I want to do Lebowski"?

He was like, "I have some ideas." He was on a plane and I was on a plane, and finally he hit me with a Lebowski picture. And I was like, What the fuck am I supposed to do with this, bro? He sent me the DVD cover—it wasn’t jewelry-friendly. So we talked a little bit and I was like, "Yo, this is going to be legendary."

What were the challenges of making this piece?

I had to make sure his hair looked three-dimensional, that it looked wavy, because it’s The Dude. I wanted to make sure he had his robe. All the diamonds are white, super high-quality, the best of the best. John will not accept anything less. Last minute, he said, "I want a little purple to represent the V-neck T-shirt he wore throughout the movie." So we went back to the drawing board. We had 90 percent completed the piece, and at the end I had to figure something out for the shirt. It was tough. We changed one thing and, to be honest, I was stumped. And John was like, "How about if we change the sunglasses?" He was like, "Ben, these are Vuarnets." And I was like, "Dude, you don’t have to tell me about Vuarnets."