Vlad Tenev, CEO and co-founder Robinhood Markets, Inc., is displayed on a screen during his company’s IPO at the Nasdaq Market site in Times Square in New York City, U.S., July 29, 2021.Brendan McDermid | ReutersRobinhood shares jumped 21% on Friday, a day after the CEO of a major crypto exchange took a stake in the retail investing app.An entity called Emergent Fidelity Technologies took a 7.6% stake in Robinhood worth $648 million earlier this month, according to a document filed with the Securities and Exchange Commission. The document also showed Sam Bankman-Fried, who leads the Bahamas-based crypto company FTX, is the sole director and majority owner of Emergent. The stake makes Emergent the third-largest Robinhood shareholder, FactSet data shows. Shares of Robinhood closed at $8.56 on Thursday, the day the document was filed. That was about 77% below the company’s July IPO price.Bankman-Fried acquired the shares because they “represent an attractive investment,” according to the filing, which also says he “intends to hold the Shares as an investment” and doesn’t have “any intention of taking any action toward changing or influencing the control of the Issuer.”He may “from time to time engage in discussions” with management, however.”Of course we think it is an attractive investment too,” Robinhood’s communications team said in a tweet Thursday evening in response to the news of the investment.Bankman-Fried can also review “options for enhancing stockholder value through, among other things, various strategic alternatives or operational or management initiatives,” according to the document. It also said he could acquire additional shares.FTX is one of the biggest crypto exchanges in the world. It offers derivatives products for more sophisticated traders, as well as spot trading, and has become a rival to big names such as Coinbase and Binance. It offers services in the U.S. through a separate entity, FTX U.S.Though Robinhood got its start in stock trading, it saw huge success when it rolled out its crypto trading platform in 2018. Crypto trading has since become important for the company’s bottom line. In the fall, Robinhood revealed its testing a crypto wallet and said the waitlist for it had topped 1 million customers.