Leslie Valiant, the 2012 recipient of the ACM Turing Award, was honored for transformative contributions to the theory of computation, including the theory of probably approximately correct (PAC) learning, the complexity of enumeration and of algebraic computation, and the theory of parallel and distributed computing.
More on Leslie G Valiant and his work can be found here.
The A.M. Turing Award, the ACM's most prestigious technical award, is given for major contributions of lasting importance to computing. Recipients are invited to give the annual A.M. Turing Award Lecture. The award is also accompanied by a cash prize of $250,000, which in recent years has been underwritten by the Intel Corporation and Google, Inc.
This site celebrates all the winners since the award's creation in 1966. It contains biographical information, a description of their accomplishments, straightforward explanations of their fields of specialization, and text or video of their A. M. Turing Award Lecture.
The A.M. Turing Award, sometimes referred to as the "Nobel Prize" of Computing, was named in honor of Alan Mathison Turing (1912–1954), a British mathematician and computer scientist. He made fundamental advances in computer architecture, algorithms, formalization of computing, and artificial intelligence. Turing was also instrumental in British code-breaking work during World War II.