Video game service Roblox listed its shares publicly on Wednesday in a highly anticipated market debut that made founder and CEO Dave Baszucki a billionaire several times over.

Baszucki, who started the company in 2004, owned 66 million shares and controlled 70% of the voting power of all Roblox shareholders, as of Jan. 15, according to the company’s regulatory filings. With the shares opening for trading at $64.50, his stake is worth almost $4.3 billion on paper.

The company already has over 32 million users a day, though most are 13 years old and younger. Up next, Baszucki tells Fortune just after the first trade was completed, is going for older kids and adults. “We’re really optimistic about all these growth opportunities,” he says. “The one we’re in the middle of now is people of all ages playing on the platform and a lot of growth in the 13-and-over segment.”

The 58-year-old Baszucki grew up in Minnesota and studied computer science and engineering at Stanford University. Before starting Roblox, he built a computer simulation for physics students called Interactive Physics that became his first software business. The idea for Roblox, which lets users make, share, and play games, came after Baszucki saw how users of the physics simulation app enjoyed sharing their creations.

His brother, Greg Baszucki, is a director of Roblox and owned 15.6 million shares of Roblox, worth $1 billion at Wednesday’s price, according to the company’s filings. Several venture capital firms that were early investors also owned large stakes: Altos Ventures owned 116.3 million shares, now worth $7.5 billion; Meritech Capital owned 55.3 million, worth $3.6 billion; and Index Ventures owned 53.1 million, worth $3.4 billion.

CEO Baszucki says his family has been discussing how to handle their newfound wealth, including millions more shares he could earn if the company hits certain performance targets. “We intend to take all of that and contribute it to philanthropy,” he says. “We have various causes that we’re interested in, ranging from education, mental health, environmental causes, that really our family is contributing to building this vision forward.”

Roblox’s debut valued the company at over $42 billion on a fully diluted basis. The company was valued at $29.5 billion for its last private fundraising in January.

Roblox decided last year not to go public using a traditional underwritten initial public offering. Instead, it directly listed already issued shares on the New York Stock Exchange.

By avoiding a traditional initial public offering underwritten by Wall Street banks, Roblox also avoided the spectacle of “leaving money on the table.” That’s when a company sells shares at its IPO price only to see the stock price immediately jump much higher on its first day of trading.

For example, Airbnb sold 50 million shares priced at $68 each in its December IPO. But the stock opened trading at $146, as many initial investors immediately sold their shares. In theory, if Airbnb could have sold its entire IPO at the higher price, it would have collected $4 billion in additional proceeds.

Baszucki says he was “overjoyed” at how the deal went down, with every prior shareholder who decided to sell, including many longtime company employees, getting the same price.

“That first trade we just did about 20 or 30 minutes ago, oh my gosh, everyone traded at that exact same price, which feels very Roblox authentic,” he says. “So we’re really happy with the way this all turned out.”

Roblox allows anyone to make games for free and sell in-game items using the company’s Robux currency. The company takes a cut of each transaction, providing its primary source of revenue. For 2020, Roblox’s revenue totaled $924 million, almost double the $508 million it made in 2019. Still, the company’s net loss increased to $253 million in 2020, up from a $71 million loss in the previous year.

More than 32 million play games daily on Roblox, and more than 8 million people have designed games or other virtual experiences. Investors expect the service, which has mainly appealed to kids so far, will extend its reach to adults with increasingly sophisticated games over the coming years.