Masayoshi Son has outgrown Japan. His $7.9 billion fortune makes the SoftBank founder and president the country's second-richest man, according the Bloomberg Billionaires Index. His upstart SoftBank Mobile won Japan's first iPhone contract in 2008 and has become the nation's fastest-growing telecom, announcing the purchase of smaller rival eAccess for $2.3 billion earlier this month.

Son, 55, also chairs Yahoo! Japan, one of the country's most powerful Internet portals and broadband providers. His influence even extends to baseball, where his Fukuoka SoftBank Hawks are defending the Japan Series championship this fall.

But Japan's aging population and stagnant economy pose challenges for almost every business, even telecoms. In the past five years, while the world's consumers swooned for the iPhone and Android smartphones, handset shipments in Japan fell by 27 percent. That helps explain Son's Oct. 15 Tokyo press conference announcing a $20.1 billion agreement to buy 70 percent of Sprint Nextel (S), the No. 3 U.S. telecom operator. If the deal clears, it will be the biggest Japanese external acquisition since at least 2000, according to data compiled by Bloomberg. Either way, it shows that Son wants a bigger spotlight than slow-growth Japan can provide. "I'm a man, and I think every man wants to be No. 1," he said, standing next to Sprint CEO Dan Hesse at the Tokyo press conference. Hesse is slated to continue in that role.