Alibaba Group, the Chinese Web juggernaut that has become the world’s biggest online retailer, will sell its first shares to the public Friday in one of the most lucrative debuts in stock market history.

Though little known in the United States, the tech powerhouse has in 15 years transformed life in China, where 80 percent of online sales pass through an Ali­baba site. Its colorful, chaotic marketplaces, where consumers can buy nearly anything, saw $248 billion in sales last year, more than and eBay combined.

Investors see the offering as a way to bet on one of the fastest-growing economies on Earth and on the future of China’s rapidly flourishing and increasingly Web-savvy middle class.

Alibaba’s new billions could also help fund its future expansion into the United States, where in the past year it has invested in tech start-ups working on ride sharing, messaging, delivery services, sports apparel, antique furniture and video games. The company’s showy debut at the New York Stock Exchange, where founder Jack Ma will ring the opening bell Friday, is the most aggressive effort yet by a Chinese company to stand shoulder to shoulder with the U.S. titans that rule the digital economy in the West.

The company, trading under the ticker symbol BABA, said Thursday that it had priced its shares at $68 each, valuing the megafirm at $168 billion — more than the value of

Alibaba could top America’s biggest IPO (The Washington Post/Source: Dealogic)

The company’s initial public offering is expected to raise $21.8 billion, although its underwriters could exercise an option to buy more shares, sending its total past $25 billion. That would better the largest U.S. IPO, Visa, which raised $19.7 billion in 2008, and the $22 billion raised by the Agricultural Bank of China in 2010.

Alibaba doesn’t own the stuff it sells. Instead, sellers pay listing fees and for ads that help them stand out among the company’s 280 million active annual users. So a U.S. business that goes to could set up a deal to buy yoga mats or hard drives from bulk suppliers around the world.

If ordinary consumers want to purchase, say, a vintage dress, a bookshelf or even a live scorpion, they could go to Alibaba’s flagship online marketplaces, Taobao and Tmall, although these sites are largely in Chinese. This year, Ali­baba also launched the invite-only shopping site, aimed at American buyers.

Beyond retail, the conglomerate has stakes in Chinese payment services (think PayPal), video streaming (think YouTube) and cloud computing. It has poured hundreds of millions of dollars into U.S. start-ups, including Uber ride-sharing competitor Lyft, delivery service ShopRunner and video-gaming venture Kabam. To compete with Chinese rivals, it has recently invested in mobile browsers, social media and film production.

Alibaba’s size and partnerships with low-cost Chinese suppliers could undercut U.S. retailers’ ability to compete on price. But analysts said Alibaba would face big challenges securing a foothold in the West, where it would need to outmaneuver the world’s leading tech titans while building an audience from scratch.

“They’re smart, they’re hungry, they’re aggressive, they can compete,” said Puneet Manchanda, a professor of marketing at the University of Michigan who has researched Taobao. “But the U.S. is a big question mark. . . . They don’t have particular expertise [here], and there’s such an entrenched competition, it’ll be hard to reach that level of dominance.”

Ma was a 34-year-old English teacher when, in 1999, he piled 17 friends into his squat Hangzhou apartment to build, a listing service for small Chinese exporters. He named it after a poor laborer in an Arabic folk tale who learns a phrase, “open sesame,” that unlocks hidden treasures.

The service launched at an opportune time for China, where a “new mainstream” of middle-class households was benefiting from rising wages and a more accessible Web. Since 1999, China’s Internet-using population has grown from 9 million to more than 600 million.

Ma, who is impish, rail-thin and famous for his outlandish performances — he once donned leather and a mohawk to croon an Elton John song in front of 16,000 employees — has become a cult figure in China on par with Microsoft’s Bill Gates or Apple’s Steve Jobs.

Ma stepped down as chief executive last year but remains both the company’s executive chairman and, at 50, one of China’s richest men, with a net worth of $21.9 billion.

The stock offering is a gold mine for Alibaba’s major investors: Web portal Yahoo, which owns about a quarter of the company, and Japanese telecom giant SoftBank, which owns nearly a third. But the company’s unusual leadership structure means Ma and top insiders will retain a lock on the company’s board of directors, undermining shareholder control.

A growing Alibaba will have to compete with longtime e-commerce rivals and established players in the industries where it is pushing to expand.

But its size could prove a liability. In a May letter to employees, Ma wrote, “Lying behind the massive allure of the capital market, there is unparalleled ruthlessness and pressure.” In a Securities and Exchange Commission filing, the company warned future investors, “We cannot assure you that we will be able to maintain our growth at these levels, or at all.”

Alibaba will also need to navigate its tricky partnership with China’s government, which exerts strong control over the country’s economy and Internet. In New York last week, Ma reportedly told investors that preserving relationships with Chinese state officials was a top priority.

“The Chinese government has to think it’s worth it to try to give enterprises like Alibaba a chance, to see if they can make sound development in the international market,” said Lu Zhengwei, a chief economist at the Industrial Bank in Fujian, China. “No particular individual is able to make a decision when billions of dollars of business are involved. It must be a decision of the Chinese government.”

After an IPO, Chinese stocks typically underwhelm, falling an average of 1 percent every year for three years, compared with 7 percent annual gains for U.S., IPOs, according to research by University of Florida finance professor Jay Ritter.

But analysts said that has done little to temper the market’s excitement about Alibaba, with more and more investors spending in hopes that they can secure a piece of China’s next big thing.

“If I was a Western investor, I’d be salivating at the prospect of getting in the market there and getting big returns, and this is one way of doing that,” said Manchanda, the University of Michigan professor. “But I would also say: If these guys were smart enough to do this out of nowhere, what does that say about China? And how can I find someone else in China to achieve the same terms as well?”

William Wan in Beijing contributed to this report.