Stephen A. Cook, a noted computer scientist.
Cook formalised the notion of NP-completeness in a famous 1971 paper "The Complexity of Theorem Proving Procedures", which also contained a proof that the boolean satisfiability problem was NP-complete. The paper left open theoretical computer science's greatest unsolved question - whether complexity classes P and NP are equivalent, the answer to which has eluded researchers since.
Cook received the Turing Award in 1982 for his discovery. His citation reads:
For his advancement of our understanding of the complexity of computation in a significant and profound way. His seminal paper, The Complexity of Theorem Proving Procedures, presented at the 1971 ACM SIGACT Symposium on the Theory of Computing, Laid the foundations for the theory of NP-Completeness. The ensuing exploration of the boundaries and nature of NP-complete class of problems has been one of the most active and important research activities in computer science for the last decade.
Stephen Cook is currently a professor in the Mathematics Department at the University of Toronto.