The savvy internet investor hit the list thanks to the growing value of his social media holdings. He divided his Digital Sky Technologies into two parts last year, taking email portal Mail.Ru public. His DST Global remains a private fund investing in global internet companies like Facebook, Zynga and Groupon. In 2009, DST paid $200 million for a stake in Facebook; this initial investment has grown an estimated five-fold since then. Next, he plans to invest in every startup that comes out of Silicon Valley-based incubator Y Combinator without reading the business plan. Former particle physicist plays chess for fun. Wife Julia is contemporary artist. Leaked documents examined by The New York Times in 2017 offer a partial answer: Behind Mr. Milner’s investments in Facebook and Twitter were hundreds of millions of dollars from the Kremlin. Obscured by a maze of offshore shell companies, the Twitter investment was backed by VTB, a Russian state-controlled bank often used for politically strategic deals. And a big investor in Mr. Milner’s Facebook deal received financing from Gazprom Investholding, another government-controlled financial institution, according to the documents. Mr. Milner’s companies came to own more than 8 percent of Facebook and 5 percent of Twitter, helping earn him a place on various lists of the world’s most powerful business people. His companies sold those holdings several years ago, but he retains investments in several other large technology companies and continues to make new deals. Among Mr. Milner’s current investments is a real estate venture founded and partly owned by Jared Kushner, President Trump’s son-in-law and White House adviser. Mr. Milner, 55, studied theoretical physics at Moscow State University before moving to the United States, where he attended the Wharton School at the University of Pennsylvania in the early 1990s and then worked for the World Bank in Washington. He returned to Russia and in the late 1990s and worked as an executive at Bank Menatep, which was founded by Mikhail B. Khodorkovsky, the oil tycoon who was stripped of his company, prosecuted and imprisoned after a televised confrontation with President Vladimir V. Putin. Mr. Milner eventually teamed with Alisher Usmanov — an Uzbek-Russian oligarch close to the Russian prime minister, Dmitri A. Medvedev — and a former Goldman Sachs executive to build a significant stake in Mail.ru, a Russian internet company that now trades on the London Stock Exchange. After the Facebook deal, Mr. Milner became a fixture in Silicon Valley, spending about $100 million on a 25,000-square-foot house in Los Altos Hills and investing $7 billion in more than 30 companies, including Spotify, Airbnb and Groupon.