As a guest on BBC Radio 4's Desert Island Discs show, Gates discussed various topics including his philanthropy work, career, personal life and the playlist he would make if he got stuck on a desert island (he's into U2 and the Hamilton soundtrack). But perhaps the most interesting nugget was how "fanatical" he was about the company — so much so that he secretly tracked employees to learn how many hours they were putting in.
"I was quite fanatical about work; I worked weekends, I didn't really believe in vacations," Gates said in the interview.
"I had to be a little careful not to try and apply my standards to how hard [my employees] worked. I knew everybody's license plates so I could look out in the parking lot and see when people came in, when they were leaving. Eventually, I had to loosen up as the company got to a reasonable size."
Gates also spoke about his childhood and his apprehension surrounding his parents' rules.
"I was a bit disruptive," Gates said, adding how his parents sent him to a child psychologist. "I started early on sort of questioning: Were their rules logical and always to be followed? So there was kind of a bit of tension there as I was kind of pushing back."
See more of Gates through the years:
As he grew up, Gates grew interested in computers and spent about four to five hours per day programming. He often skipped gym class to work on computers, he said in the interview, but that eventually paid off; Microsoft boomed before he was old enough to rent a car.
In 2000, Gates stepped down as CEO of his company and started the Bill and Melinda Gates Foundation with his wife. He responded to some of the foundation's criticisms for its focus areas.
"We believe in giving women contraception, and the use of science, including [genetically-modified organism] seeds," he said. "We think that's very important because we're trying to stop malnutrition and the safety's been proven."