Bill Gates is an American businessman and philanthropist who co-founded Microsoft, the world's largest personal computer software company. As the chairman and CEO of Microsoft, Gates led the company to dominate the personal computer operating system market with MS-DOS in the 1980s and Windows in the 1990s. He stepped down as CEO in 2000 and as chairman of Microsoft in 2014. Gates is consistently ranked among the world's wealthiest people and was the wealthiest overall from 1995 to 2009. He has donated billions to charity through the Bill & Melinda Gates Foundation, which works to save lives and improve global health.