William Henry "Bill" Gates III (born October 28, 1955) is an American business magnate, philanthropist, and chairman of Microsoft, the software company he founded with Paul Allen. He is ranked consistently one of the world's wealthiest people and the wealthiest overall as of 2009. During his career at Microsoft, Gates held the positions of CEO and chief software architect, and remains the largest individual shareholder with more than 8 percent of the common stock. He has also authored or co-authored several books.

Gates is one of the best-known entrepreneurs of the personal computer revolution. Although he is admired by many, a number of industry insiders criticize his business tactics, which they consider anti-competitive, an opinion which has in some cases been upheld by the courts (see Criticism of Microsoft). In the later stages of his career, Gates has pursued a number of philanthropic endeavors, donating large amounts of money to various charitable organizations and scientific research programs through the Bill & Melinda Gates Foundation, established in 2000.

Bill Gates stepped down as chief executive officer of Microsoft in January, 2000. He remained as chairman and created the position of chief software architect. In June, 2006, Gates announced that he would be transitioning from full-time work at Microsoft to part-time work and full-time work at the Bill & Melinda Gates Foundation. He gradually transferred his duties to Ray Ozzie, chief software architect and Craig Mundie, chief research and strategy officer. Gates' last full-time day at Microsoft was June 27, 2008. He remains at Microsoft as non-executive chairman.