Daniel Nigro vividly recalls the moment his obsession with pop music started. While in sixth grade, he heard Nirvana's “Smells Like Teen Spirit” for the first time; soon after, he and his friends made their own music video to the hit through an attraction at Long Island’s Adventureland.

“Even making a fake music video, I was like, ‘Oh yeah, I want to be playing for people,” says Nigro. But after fronting the indie-rock act, As Tall As Lions, which disassembled in 2010, he had another realization: “I’m actually not that good at this, and also don’t really enjoy it.”

Later that year, he visited a friend in Los Angeles to make music for an intended solo project, and ended up joining some pop songwriting sessions as well. “It was the first time in probably years that I had fallen in love with making music again,” Nigro recalls, adding he spent those early days writing closely with his childhood best friend, Justin Raisen, and eventual indie-pop superproducer Ariel Rechtshaid. “I just realized how much I enjoyed being in a room where I could create music and not feel it was so intensely me. That’s where everything changed.”

Soon enough, he was landing credits with Kimbra and Sky Ferreira. Now, he’s worked with big hitmakers like Carly Rae Jepsen, Lewis Capaldi and Finneas O’Connell, among many others. Nigro says over the last four years, specifically, he’s discovered his biggest asset is “helping artists who have a lot to say navigate their sonic landscapes." As a result, has gotten in early with some of pop’s biggest newcomers -- including Olivia Rodrigo, whose breakthrough single "Drivers License" he co-wrote and produced -- crafting hits in his 200 square-foot L.A. garage ever since.

Below, Billboard catches up with Nigro below to discuss some of the biggest songs he's worked on -- including, of course, the biggest song in the world for the last four weeks.

Caroline Polacheck, "So Hot You're Hurting My Feelings"

While working together on Polacheck’s debut album, 2019’s Pang, Nigro recalls her walking in with the fully formed concept for this track. “She literally came into the room and said, ‘I want to write a song called, ‘So Hot You're Hurting My Feelings,’ and we were just like, ‘Let's go.’” He says the project was shaping up to be a moody, darkly colored world, which helped inspire them to create something a bit more fun: “I felt there was this moment where we were like, ‘Can we not make something heavy?” He says the writing process (which included working with pop/rock behind-the-scenes regular Teddy Geiger) for the entire song minus the bridge took just two hours. “It was just like, ‘Oh wow, we did something [fun] -- and it felt good.’"

Conan Gray, “Heather”

Nigro has always gravitated towards “music you listen to by yourself,” and says he’s often trying to help create those moments in an artist’s song -- which is exactly what informed the process of “Heather,” off Conan Gray’s 2020 debut full-length Kid Krow. “The vision was to keep it as cinematic as possible and also to keep the vocal almost uncomfortably in your face,” he says. “I was like, ‘I want it to feel like you’re in the room and hearing this person talking to you,’ in terms of the verse.”

Though “Heather” was a favorite within Conan’s team, the plan was never to work it as a single. As a result, Nigro says “we just did whatever we wanted to do,” including tacking on a 25-second intro. “I always laugh because it's his biggest song -- and people always talk about Spotify analytics and how songs shouldn't have this long of an intro and it always pisses me off. I have to constantly remind myself, even though I don't abide by that rule, 'Just make the song [you want].'"

Claud, "Soft Spot" 

The same friend who turned Nigro on to Conan Gray, A&R Max Wang, also introduced him to Claud, an emerging singer-songwriter signed to Phoebe Bridgers’ label Saddest Factory. Nigro says the first day they were scheduled to meet and write together, though, at the top of 2020, he was feeling quite introverted and nervous he wouldn’t be of any help. “But they came in and said, ‘I have this idea to write a song called “Soft Spot."' All of a sudden, it just flowed out and I remember feeling relieved that they had had the spark of inspiration, because I wasn't feeling like I was going to be the one to come in with one.”

Nigro says he's has gotten better over the years at voicing when a session feels right or wrong, saying “sometimes you rise to the occasion and end up pushing through the awkwardness, but I've learned that over the years that there are tons of times where you fight through it just to, for a lack of a better word, be nice. I started to realize after a while, ‘Don't force the awkwardness.’ After you've been sitting in a room for two or three hours and you're not getting something [it’s OK to admit], 'Hey, I don't know if we're compatible.'”

Olivia Rodrigo, “drivers license” 

Nigro says since working with Grey, his inbox is filled daily with new artists' pitches -- but Olivia Rodrigo immediately captured his attention. He quickly went on her Instagram and found a clip of a song called “Happier,” saying, “I just got the chills and I was like, ‘Oh my God, her voice is insane.’ I literally DM’d her that second and was like, ‘Hey, I think you're amazing. We should make music.’”

The pair met soon after, but then pandemic hit and halted their plans. Months later, after a series of safety procedures, they were able to hunker down at Nigro’s home studio to start working on new material. Eventually, Rodrigo started bringing in half-baked ideas, one of which was “Drivers License.” He says he and Rodrigro share the same “how do we make this better?” mentality, “so we constantly were questioning everything about it,” from whether or not the drums come in too late (they don’t arrive until the bridge) to having Rodrigo resign the vocals in full and head voice, “going back and forth to see what the right emotion should be.”

Now, looking back, he says that while they both love the song, “neither of us thought it was going to do what it did” -- which includes topping the Hot 100 for four weeks and counting, and raking in 76.1 million streams in its first week, the best sum since Cardi B and Megan Thee Stallion's "WAP." Adds Nigro: "I don't think our expectations were even 1/20th of where it is."

A version of this article will appear in the Feb. 20, 2021 issue of Billboard.