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Alonzo Church

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Alonzo Church (June 14, 1903 – August 11, 1995) was an American mathematician and logician who was responsible for some of the foundations of theoretical computer science. Born in Washington, DC, he received a bachelor's degree from Princeton University in 1924, completing his Ph.D. there in 1927, under Oswald Veblen. After a postdoc at Göttingen, he taught at Princeton, 1929-67, and at the University of California, Los Angeles, 1967-90.

Church is best known for the following accomplishments:

His proof that Peano arithmetic and first order logic are undecidable. The latter result is known as Church's theorem.
His articulation of what has come to be known as Church's thesis.
He was the founding editor of the Journal of Symbolic Logic, editing its reviews section until 1979.
His discovery of the lambda calculus.

The lambda calculus emerged in his famous 1936 paper showing the existence of an "undecidable problem". This result preempted Alan Turing's famous work on the halting problem which also demonstrated the existence of a problem unsolvable by mechanical means. He and Turing then showed that the lambda calculus and the Turing machine used in Turing's halting problem were equivalent in capabilities, and subsequently demonstrated a variety of alternative "mechanical processes for computation" had equivalent computational abilities. This resulted in the Church-Turing thesis.

The lambda calculus influenced the design of the LISP programming language and functional programming languages in general. The Church boolean is named in his honor.

Church's doctoral students were an extraordinarily accomplished lot, including C. Anthony Anderson, Martin Davis, Leon Henkin, John George Kemeny, Stephen Kleene, Michael O. Rabin, Hartley Rogers, Jr, J. Barkley Rosser, Dana Scott, Raymond Smullyan, and Alan Turing. See [1].