William Henry Gates III, born on October 28, 1955, is an American businessman and philanthropist. He co-founded the software company Microsoft in 1975 with his childhood friend Paul Allen, pioneering the microcomputer revolution of the 1970s and 1980s. Gates served as Microsoft's CEO for 25 years and also became president and chairman of the board in 1981. He became the world's then-youngest billionaire in 1987 at age 31, following Microsoft's initial public offering.