Best known for being one of the inventors of the RSA algorithm with Len Adleman and Adi Shamir

Wikipedia: http://en.wikipedia.org/wiki/Ron_Rivest

Turing Award Winner, 2002:http://amturing.acm.org/award_winners/rivest_1403005.cfm

Inducted into the (US) National Cyber Security Hall of Fame 2012 http://www.cybersecurityhalloffame.com/

From the Cyber Security Hall of Fame page:

Professor of Computer Science at MIT's EECS Department

"He is the Andrew and Erna Viterbi Professor of Computer Science at MIT's Department of Electrical Engineering and Computer Science (EECS) and a member of MIT's Computer Science and Artificial Intelligence Laboratory (CSAIL) 

"Rivest is a member of the National Academy of Engineering, the National Academy of Sciences, and is a Fellow of the Association for Computing Machinery, the International Association for Cryptologic Research, and the American Academy of Arts and Sciences"