Motwani, 47, was best known for helping two Stanford graduate students create Google, but Brin says there was so much more to this man.
"That happens to get a lot of attention, but any kind of technology you use today, your computer, you're phone, any website and what not, it's very likely that some little piece of that was brought to you by Rajeev Motwani," says Brin.
Motwani died on Friday in what his friends describe as a tragic accident. They say he fell into his backyard pool in Atherton and drowned on one of the rare nights his fence wasn't closed. He didn't know how to swim.
"It appears he just got disoriented very late at night. He would often go out into the backyard at night, and so was out, the lights were off," said Asheem Chandna, a family friend.
The news has really hit Silicon Valley hard. So many people stopped by his home to offer their condolences. His widow had to put up a sign thanking everyone, but asking them to come back at another time.
"Rajeev was both a brilliant man and brilliant computer scientist, but he was also a really good person," said Brin.
Motwani was a computer science professor at Stanford who loved to mentor. Angel investors say his death will leave such a void in Silicon Valley that other investors are now going to have to step up and help entrepreneurs get their ideas off the ground.
"He had a very rare ability to be able to talk to Sergey Brin and help them make their idea or vision better and real," said Chandna.
"I think he's a real model for how to remain humble and unaffected by the great success that he had," said Georges Harik, an investor, friend, and colleague.
The family will hold a private service for Motwani, but there will be a public memorial held at Stanford. The date and time for the public memorial has not yet been set.