Read the letter Bill Gates sent to Microsoft employees for the company's 40th anniversary

On April 4th, 1975, Bill Gates and Paul Allen started a little company named Microsoft. You probably know the story from there: Gates went on to become the wealthiest man in the world, and then gradually pulled back from his company to focus on broad philanthropic efforts through the Bill & Melinda Gates Foundation. But Gates is far from finished at Microsoft; last year after Satya Nadella took over as CEO, Gates said he would be taking a bigger role at the company — using up to a third of his time to advise Microsoft employees on new products.