Craig Silverstein, the first employee hired by Google co-founders Sergey Brin and Larry Page, will leave the search giant for Khan Academy, an online education portal based in Mountain View, Calif.

Craig's been with Google since the early days, said a Google spokesperson. He was instrumental in the development of search and made numerous contributions to Google over the years. We wish him all the best at the Khan Academy and know that he will do great things to help them promote education around the world.

News of Silverstein's departure first appeared yesterday in EdSurge, a newsletter on education and technology entrepreneurship. Google confirmed the news with the folks at AllThingsD.

Silverstein had been with Google shortly after it first launched in the garage of Susan Wojcicki, a friend of both Page and Brin, in September 1998. Before he joined the company, Silverstein was a PhD student at Stanford researching machine algorithms and techniques for data mining and information retrieval. He helped Brin and Page develop infrastructure when Google was just a Stanford graduate school project operating out of their dorms. When he officially joined Google, Silverstein became its technology director.

I certainly didn't imagine it would be the size it is today, Silverstein said. What are the odds?

Silverstein figured he would stay at Google for four or five years, but when the company began rapidly growing, his ideas of quitting went out the window.

It's become easier to take vacations, Silverstein said during Google's hiring spree.

In 2008, Silverstein had no plans to leave Google, but he had said he might leave the company momentarily to finish grad school or become a stay-at-home father. He decided to stay with Google at the time to improve its search engine and help mentor the company's thousands of engineers.

We need to make search as good as a human answering a search request, Silverstein said. We need to be like the computer on 'Star Trek,' and we are very, very far from that.

The Khan Academy, where Silverstein is heading, is a not-for-profit organization that aspires to change the education industry by providing free world-class education to anyone anywhere. Microsoft Chairman Bill Gates is an enormous fan of the service, telling CNN that he uses it with his children.

The Khan Academy offers an extensive library of 2,800 videos, covering subjects like K-12 math, finance, history and physics, and even offers practice exercises to apply what you've learned. As you progress, the Khan Academy remembers what you've learned and where you've spent your time, and uses the data to create charts and infographics to illustrate your progress.

It is not certain how Silverstein will contribute to the Khan Academy, but he will go from working alongside tens of thousands of employees to just 21.