As a 13 year-old in Seattle, Bill Gates wrote a program for playing nought and crosses against a computer.

When he met Paul Allen, one of their first ventures together was exploiting software glitches to gain free computer time from the company that supplied their school equipment.

Then they developed a computer program to monitor Seattle’s traffic, earning them $20,000 aged 15. Though they wanted to start a business together, Gates’ parents insisted he went to university, and he enrolled at Harvard to study law.

His future was transformed by an article in Popular Electronics magazine about the Altair 8800 mini-computer kit. Showing the confidence which helped his business to survive in its early days, Gates contacted the manufacturer and offered them a software program to run the computer. The program didn’t exist, and Gates didn’t even own an Altair computer.

When the company showed an interest, Gates and Allen spent two frantic months developing the program.

Soon after, Gates left Harvard and the two men founded Microsoft. With 1.2 billion users of Microsoft Office, and annual revenue in FY2018 of $110.36bn, it’s a business that’s definitely thriving.