Gates was born William Henry Gates III on October 28, 1955, in Seattle, Washington. Gates grew up in an upper-middle-class family with his older sister, Kristianne, and younger sister, Libby. Their father, William H. Gates Sr., was a promising, if somewhat shy, law student when he met his future wife, Mary Maxwell. She was an athletic, outgoing student at the University of Washington, actively involved in student affairs and leadership.

The Gates family atmosphere was warm and close, and all three children were encouraged to be competitive and strive for excellence. Gates showed early signs of competitiveness when he coordinated family athletic games at their summer house on Puget Sound. He also relished in playing board games (Risk was his favorite) and excelled at Monopoly.

Gates had a very close relationship with his mother, Mary, who after a brief career as a teacher devoted her time to helping raise the children and working on civic affairs and with charities. She also served on several corporate boards, including those of the First Interstate Bank in Seattle (founded by her grandfather), the United Way and International Business Machines (IBM). She would often take Gates along when she volunteered in schools and at community organizations.

Gates was a voracious reader as a child, spending many hours poring over reference books such as the encyclopedia. Around the age of 11 or 12, Gates's parents began to have concerns about his behavior. He was doing well in school, but he seemed bored and withdrawn at times, and his parents worried he might become a lo

Though they were strong believers in public education, when Gates turned 13, his parents enrolled him at Seattle's exclusive preparatory Lakeside School. He blossomed in nearly all his subjects, excelling in math and science, but also doing very well in drama and English.

While at Lakeside School, a Seattle computer company offered to provide computer time for the students. The Mother's Club used proceeds from the school's rummage sale to purchase a teletype terminal for students to use. Gates became entranced with what a computer could do and spent much of his free time working on the terminal. He wrote a tic-tac-toe program in BASIC computer language that allowed users to play against the computer.

Gates graduated from Lakeside in 1973. He scored 1590 out of 1600 on the college SAT test, a feat of intellectual achievement that he boasted about for several years when introducing himself to new people.