Rohan Seth realized that Clubhouse was having a moment when Oprah showed up.

It was June 2020 when the queen of talk took to Clubhouse, the hot social media app Seth cofounded, to discuss criminal justice reform with author and motivational speaker Shaka Senghor. Although Clubhouse had grown steadily since its debut in March 2020, it wasn’t attracting the kind of buzz that other now well-known Internet startups had over the years. It was a pivotal moment for Clubhouse because Oprah would undoubtedly draw attention to the app, which powers hundreds of thousands of “rooms” for what are essentially live podcasts.

But Clubhouse was still tiny. The only employees were Seth and cofounder and CEO Paul Davison, plus a “couple of folks” who were helping out, Seth told Fortune. Three hundred people listened to Oprah powwow with Senghor and others including broadcast journalist Gayle King and entertainment mogul Michael Ovitz. The two cofounders were worried the service might crumble under pressure, technically speaking. Thankfully, there were no problems; Oprah was pleased, and the app didn’t crash.

“I remember calling Paul after the room ended and was like, ‘The servers are good. Wow this is such a great thing,’” Seth recalled.

Although Seth said he’s “not a great engineer,” the technologist must be doing something right. That Clubhouse hasn’t experienced any major technical hiccups since ballooning to over 10 million weekly active users and hosting 700,000 rooms daily is noteworthy, explained Stephanie Chan, a mobile insights strategist at analytics firm Sensor Tower.

“If your app is buggy—it doesn’t work, it’s difficult to use, and there’s privacy concerns—that’s a lot more of an immediate block,” Chan said about how tech problems could quickly tarnish the reputations of new social media services.

Seth’s combination of product and tech chops coupled with an entrepreneurial drive helped get him on Fortune’s annual 40 Under 40 list. He’s helping steer one of the most talked-about consumer apps in recent years at a crucial time in its history. Investors have plunked over $300 million in the startup, which now has a private valuation of $4 billion, according to deal-tracking service PitchBook.

Still, Clubhouse faces an unpredictable future in a fiercely competitive industry. Giants like Facebook, Amazon, Spotify, and a growing roster of startups are increasingly stepping on its audio turf.

Besides leading Clubhouse, Seth and his wife helped create the Lydian Accelerator health care nonprofit, named after his daughter, Lydia, who has a genetic disease. The accelerator’s goal is to encourage scientists worldwide to work on and share research about uncommon genetic disorders that major pharmaceutical companies may overlook.

“We said, ‘Let’s try to start an organization,’” Seth recalled. “‘We know it’s gonna be expensive. Let’s raise money for it, and let’s figure out how do we do something for Lydia.’”

From a Jim Carrey fan site to Clubhouse

A self-described “product builder,” Seth said he was always interested in creating things, and he remembered doing carpentry as a child in India, where he grew up. After he got his first computer at 13, he said he started building websites and was captivated by the idea that he could connect with people all around the world.

Two websites stand out from his past: One was dedicated to the 1990s science-fiction cult hit The X-Files, and the other was a shrine to the comedian and actor Jim Carrey. Seth said his colleagues still occasionally rib him for his fan site in tribute to the Ace Ventura star.

“Hi, I’m Rohan. I’m 13 years old, and Jim Carrey is my favorite actor!” Seth said of his website’s dork quotient at the time.

In 2002, Seth left India for the U.S. to study computer science at Stanford University and got a job at Google during his junior year. At the search giant, he worked as a software engineer on several projects, including the Google Latitude feature that let mobile users view and share their location with others through Google Maps.

In 2012, Seth left Google to build his own startup, Memry Labs, where he oversaw the development of several social apps that never caught on. After a few years of tinkering, he sold the company to the real estate tech firm Opendoor, where he worked for a few years. Still, Seth yearned to create another startup, and he found a partner in Davison, who had built a social app called Highlight, which was eventually acquired by Pinterest.

When the two started brainstorming startup ideas, they didn’t want anything to do with social media, Seth said, citing the difficulty of creating a buzzy app.

“We’re both old. I’ve got a daughter, he’s got three kids,” Seth said. “And, you know, let’s do something a little bit more predictable. It’s not rational to work on social.”

But the duo ultimately decided to tackle social media after noting the rise of audio, which they felt “was at this inflection point” thanks to voice-activated digital assistants like Amazon’s Alexa, Internet-connected smart speakers, and the growing popularity of Apple’s AirPods. The two eventually came up with the idea of the core Clubhouse app, where people could gather and network, or listen to others talk as if they were conference keynote speakers.

Andy Miah, a professor and chair in science communication and future media at the University of Salford, in the U.K., credits Zoom fatigue during the COVID-19 era as contributing to Clubhouse’s ascent. That Clubhouse doesn’t bombard people with online ads also helps the service stand out from other social media apps, Miah said.

“I think Clubhouse just harkens back to maybe a more naive or perhaps a better time when the Internet was about just talking to each other without interference,” Miah said.

Helping Lydia and giving hope to others

After Seth’s daughter, Lydia, was born two and a half years ago, she began having seizures. A genetic test a few weeks later found that Lydia “had a spontaneous mutation in a gene that would cause severe lifelong physical and mental disabilities,” he said.

“It’s devastating as parents, you know, first-time parents,” Seth said. “My wife and my way of coping with it was throwing ourselves into the research and trying to understand what can we do.”

He said they learned that “there was actually technology that existed that could silence some of these mutations at the RNA level.” When they asked experts about why the possible treatment was unavailable for Lydia, Seth recalled they would tell him that “Lydia’s mutation is too rare” and that there were “only two other patients with her mutation.”

He added that it didn't make sense to him and his wife to describe the disorder as an anomaly.

"There are 6 billion characters of code in our DNA, any mutation in them was statistically likely to be rare," Seth said. "But collectively there are millions. We needed to have a platform approach to fix each mutation."

Seth and his wife eventually learned that there was a scientist working on research that could help Lydia’s disorder. Although the research was still early, “I think that’s all the hope that you need as a parent, right?” he said.

He spent all of 2019 working on the Lydian Accelerator, establishing connections with more scientists and geneticists who could team up and conduct the time-consuming experiments needed to learn more about these rare disorders.

“We have a good process, but we’re certainly behind in terms of what I hope we would have had for Lydia by now,” Seth said. “And most of that was because biology is slower than social networks. There’s a lot of trial and error.”

He’s hopeful that any research and treatments that sprout from the Lydian Accelerator will help newborns, because “the advantage of these solutions usually happens when you’re really young, like days of life.”

As for Lydia, she is “probably operating at about a 6-month-old, mentally,” and although she doesn’t know her name, she smiles at her parents and expresses happiness, Seth said.

Through their research, Seth said he and his wife found a drug that they administered to Lydia when she was around 4 months old, which he attributed to helping improve her physical development. Prior to the drug, Seth said he didn’t know if Lydia would be able “to sit, crawl, walk—any of those things.”

But the treatment, he said, has been a game changer for Lydia.

“She started walking a couple of months ago,” Seth said.