Gates' and Buffett's friendship dates back to July 5, 1991. Gates' mother, Mary, had invited the late Meg Greenfield, a Washington Post editor, to her home. Greenfield was to bring her friend Buffett with her.
Mary Gates pressed her son to join them — he didn't want to take the day off work. "What were he and I supposed to talk about, P/E ratios?" Gates later wrote. The only reason he decided to come was because Greenfield was also bringing the late Post publisher Katharine Graham and he was interested in the Post's history.
Buffett didn't particularly want to meet Gates, either. "While we're driving down there, I said, 'What the hell are we going to spend all day doing with these people? How long do we have to stay to be polite?" Buffett remembered years later.
To the surprise of both men, they hit it off. Gates recalls being impressed by the questions Buffett asked him, like, "If you were building IBM from scratch, how would it look different?" And Gates told Buffett to buy stock in Intel and Microsoft. It was the beginning of a deep friendship and a mutual mentorship.
Shortly after that first meeting, Gates asked Buffett for his favorite business book recommendation. Buffett lent Gates his copy of "Business Adventures" by John Brooks. Today, it's Gates' favorite business book, too — and he still has Buffett's copy.
Both credit their tremendous success to their laser focus. Gates has written that he's learned from Buffett how to manage his time by prioritizing certain people and tasks.
They've often joined forces for political and philanthropic causes. In 2010, Gates and Buffett, along with Gates' wife, Melinda, started The Giving Pledge. Billionaires who sign up commit to giving away more than half their wealth.