Japan’s SoftBank Corp (9984.T) plans to acquie 70 percent of Sprint Nextel Corp. (NYSE: S) in a $20.1 billion deal, Sprint announced in a joint statement on Monday.

The deal is expected to help Sprint, of Overland Park, Kan., deploy a more integrated next-generation wireless network in an effort to wrest market share from its two larger competitors in the U.S. mobile market: the Verizon Wireless unit of Verizon Communications Inc. (NYSE: VZ) and AT&T Inc. (NYSE:T).

The announcement sent Sprint’s stock price to $5.78 in opening trading on Monday, just above the acquisition price. SoftBank’s shares declined 5 percent in Tokyo on Monday to ¥2,268 ($28.81). Softbank’s share price has lost more than 20 percent since Friday after rumors of the deal.

Mizuho Financial Group Inc., Sumitomo Mitsui Financial Group, Mitsubishi UFJ Financial Group and Deutsche Bank will provide $21.1 billion in loans to fund the deal, the company said.

“This transaction provides an excellent opportunity for Softbank to leverage its expertise in smartphones and next-generation high-speed networks,” said SoftBank CEO Masayoshi Son, the 55-year-old Korean-Japanese billionaire.

Son is one of Japan’s more outspoken and garrulous corporate executives who talks enigmatically about having a 300-year vision for his company. He recently unveiled the world’s first mobile phone with a built-in Geiger counter -- a nod to Son’s personal mission to expand his country’s renewable energy sources following last year’s Fukushima Dai-Ichi nuclear plant accident.

While attending the University of California at Berkeley, Son invented a voice-operated multilingual translator that he sold to Sharp Corp.  (TYO: 6753) for 100 million yen in 1979 -- one of several patents Son has filed. He made one of his first bundles of cash importing and renting U.S.-made coin-operated Space Invaders video games to restaurants, seeing early on the oncoming Japanese infatuation with computer-based entertainment. (Ironically, the game was created by the famous designer of Osaka, Tomohiro Nishikado; the machines themselves were built by Bally Technologies Inc. of Las Vegas.)

In 2006, Son acquired all of Vodafone Japan from Vodafone Group of the UK (Nasdaq: VOD) for $15 billion, one of the largest acquisitions for a Japanese company to date. Softbank had been a partner with Vodafone Group, but Vodafone Japan was shedding customers, attributed largely to the British-based company’s inability to adapt to the specific demands of Japanese mobile phone customers, who tend to be eager early adopters of new mobile technologies.

Vodafone was quickly rebranded as  Softbank Mobile Corp. In 2008, Son won an exclusive deal to sell iPhones from Apple Inc. (Nasdaq: AAPL) in Japan, beating Tokyo-based NTT Docomo Inc (TYO: 9437). According to a Forbes magazine profile, Son’s friendship with Apple CEO Steve Jobs was instrumental.

Competitor KDDI Corp (Tokyo: 9433) began selling the iPhone last October, but Son’s ability to land the iPhone deal gave Softbank a four-year head start into the market before a competitor was able to offer the popular smartphone.

In addition, Softbank under Son’s control was instrumental to making Yahoo Japan more of a success than the Internet company’s other country portals. While Yahoo Inc.’s  (NASDAQ: YHOO) other country portals lagged against Google Inc. (NASDAQ: GOOG), Yahoo Japan gained market share under Son’s controlling stake in the joint venture.

Son reportedly dismissed Yahoo’s global strategy, likening it to having “one smart guy” in California running “those slaves in the poor countries.” Yahoo, of Sunnyvale, Calif., has had a new CEO, Marissa Mayer, since July.

The 2011 Tōhoku earthquake and tsunami rattled Son’s conscience. He not only gave $119 million to relief operations and pledged his future Softbank salary to orphans, but also become one of the country’s outspoken proponents for replacing nuclear energy with wind and solar infrastructure. As the public read about radiation from the Fukushima Dai-Ichi nuclear plant speared to over 230 square miles, Son announced a major initiative to build solar power plants with the cooperation of 33 of the country’s prefectures.