Best known for being one of the inventors of the RSA algorithm with Ron Rivest and Len Adleman

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

Turing Award Winner, 2002: http://amturing.acm.org/award_winners/shamir_2327856.cfm

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

From the Cyber Security Hall of Fame page:

Faculty of Mathematics and Computer Science at the Weizmann Institute

"He is a co-inventor of the RSA algorithm (with Ron Rivest and Len Adleman), a co-inventor of the Feige–Fiat–Shamir identification scheme (with Uriel Feige and Amos Fiat), one of the inventors of differential cryptanalysis and has made numerous contributions to the fields of cryptography and computer science 

"In addition to RSA, Shamir's other numerous inventions and contributions to cryptography include the Shamir secret sharing scheme, the breaking of the Merkle-Hellman knapsack cryptosystem, visual cryptography, and the TWIRL and TWINKLE factoring devices. 

"Shamir has also made contributions to computer science outside of cryptography, such as finding the first linear time algorithm for 2-satisfiability and showing the equivalence of the complexity classes PSPACE and IP."