Microsoft’s 50-year rise was steered by just four leaders whose distinct visions transformed it from a startup into a $3 trillion titan.

When Bill Gates and Paul Allen founded the company they called Micro-Soft 50 years ago this week, it was to sell a version of the Basic computer language for the Altair, the first proto-PC. Their first product set the pattern for what was to follow.

In the spring of 1975, a college dropout and his childhood friend launched a tiny software company in Albuquerque with a singular mission: put a computer on every desk and in every home. Five decades later,