Steve Ballmer

Steve Ballmer is the high-energy former CEO of Microsoft, who led the company from 2000 to 2014.

He joined Microsoft in 1980 as employee No. 30 after dropping out of Stanford's MBA program. He first met Microsoft cofounder Bill Gates when the two were undergrads at Harvard.

Ballmer oversaw Microsoft after the first dot-com crash and through efforts to catch up to Google in search capabilities and Apple in mobile phones.

In 2014, the year he retired from Microsoft, he bought the NBA's Los Angeles Clippers for $2 billion; Forbes now values the team at $7.5 billion. He spent another $2 billion building a stadium.

Ballmer, who owned 4% of Microsoft stock when he retired, has held onto most of his stock and has said he's the company's largest individual shareholder.

He has ramped up his philanthropy since 2014; to date the Ballmers have given away more than $6.5 billion.