Bill Gates III is the co-founder of Microsoft and is an American business magnate, investor, author and philanthropist. In 1975, Gates and Paul Allen co-founded Microsoft, which became the world's largest PC software company. During his career at Microsoft, Gates held the positions of chairman, CEO and chief software architect, while also being the largest individual shareholder until May 2014. Gates is one of the best-known entrepreneurs of the personal computer revolution. Since 1987, Gates has been included in the Forbes list of the world's wealthiest people. As of May 2017 Gates is the richest person in the world, with an estimated net worth of US$88.5 billion. In 2009, Gates and Warren Buffett founded The Giving Pledge, whereby they and other billionaires pledge to give at least half of their wealth to philanthropy. Gates scored 1590 out of 1600 on the Scholastic Aptitude Tests and enrolled at Harvard College in the fall of 1973. While at Harvard, he met fellow student Steve Ballmer. Gates left Harvard after two years while Ballmer would stay and graduate magna cum laude. Years later, Ballmer succeeded Gates as CEO of Microsoft before resigning from the company in 2014