Rajeev Motwani, 47, the Stanford University computer science professor who mentored Google's founders when they were graduate students, apparently drowned Friday in the swimming pool at his Atherton, Calif., home.

Friends said he did not know how to swim, but was planning on taking lessons. They speculated he may have fallen in the pool overnight; he often stayed up late exchanging e-mails.

The news of his death struck like a thunderclap in Silicon Valley. Blogs, Facebook pages and Tweeter communications were filled with testimonials to a brilliant, kind man who was never too busy to help a budding entrepreneur or struggling graduate student. He helped many startups gain a foothold, but none so famous as Google.

"Today, whenever you use a piece of technology, there is a good chance a little bit of Rajeev Motwani is behind it," Google co-founder Sergey BrinBrin wrote in his blog.

Motwani's work had a major effect on the field of algorithms, and he used his knowledge of that field to develop methods for searching almost infinite archives of data by randomly selecting subsets of the data. It was in the field of data mining that he made some of his seminal contributions. The field is the basis of much of modern Internet commerce.

Motwani won the highest honor in computer science, the Goedel Prize, and he also earned an Alfred P. Sloan Research Fellowship.

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