Billionaires Warren Buffett and Bill Gates have been friends for twenty-five years, meeting for the first time on July 5, 1991.

In a blog post on Tuesday celebrating their friendship, Gates wrote that his mom asked him to meet Buffett at their vacation home in Washington state.

Gates didn’t want to go.

“Look, he just buys and sells pieces of paper. That’s not real value added. I don’t think we’d have much in common,” he told her.

The self-described “technology nerd” finally agreed to stop by, but only planned to spend two hours with this investor from Omaha before going back to work.

Upon meeting, Buffett immediately began asking Gates questions about Microsoft and they hit it off.

“These were amazingly good questions that nobody had ever asked,” Gates wrote. “We were suddenly lost in conversation and hours and hours slipped by. He didn’t come across as a big-shot investor. He had this modest way of talking about what he does. He was funny, but what impressed me most was how clearly he thought about the world. It was a deep friendship from our very first conversation.”

These days, Gates has two numbers on his speed-dial on his work phone— home and Buffett. Those conversations with Buffett are the “highlight” of his week.

“I’m constantly learning things from him. Warren and I love to talk about companies, politics, world events, and new innovations. And it’s really exciting to have somebody who’s studying these things with a bit of a different background. He’s got that economic investor’s eye and I have much more of a technologist’s eye towards things.”

Gates continued: “As trustee of our foundation, Warren is an amazing thought partner to Melinda and me. When faced with a challenge, we often ask ourselves, “What would Warren do?” It usually leads us to the best answer. Warren and I are mostly peers, but sometimes he is so much wiser than I am, he’s like a father figure to me.”

Above all, Gates writes that Buffett has taught him what it means to be a friend.

“Warren earned a reputation as the ‘Oracle of Omaha’ for his shrewd approach to investing in business. But he’s equally gifted at investing in people. I’m always amazed how he is able to draw people in and make it fun for them to learn from him. Even though he keeps up a hectic schedule, Warren finds time to nurture friendships like few other people I know. He picks up the phone and calls to say hello. He regularly sends articles he’s read in the mail that he thinks Melinda or I will find interesting.”

He continued: “I’ve learned many things from Warren over the last 25 years, but maybe the most important thing is what friendship is all about. It’s about being the kind of friend you wish you had yourself. Everyone should be lucky enough to have a friend who is as thoughtful and kind as Warren. He goes out of his way to make people feel good about themselves and share his joy about life.”