Gates was born on October 28, 1955 in Seattle, Washington, to William H. Gates, Sr. and Mary Maxwell Gates. His ancestry includes English, German, and Scots-Irish.

His father was a prominent lawyer, and his mother served on the board of directors for First Interstate BancSystem and the United Way. Gates's maternal grandfather was JW Maxwell, a national bank president. Gates has one elder sister, Kristi (Kristianne), and one younger sister, Libby. He was the fourth of his name in his family, but was known as William Gates III or "Trey" because his father had the "II" suffix.

Bill Gates' Family Tree