The reasons for Ballmer's retirement remain fuzzy, but there are indications that Ballmer and Gates thought it was time for Ballmer to move on.
A lot of people are calling for Gates to replace Ballmer as CEO. He founded
He's unlikely to return as CEO. While he remains chairman at Microsoft, he left the company in 2008 to focus on his foundation, which is doing good around the world.
In appreciation of Gates, here's a look back at his life.