Alonzo Church was born on June 14, 1903 in Washington, D.C., and died on August 11, 1995 in Hudson, Ohio. He spent most of his career at Princeton University, where he became one of the central figures in twentieth-century mathematical logic and a founder of what would become theoretical computer science.
During the 1930s Church developed the lambda calculus, a formal notation for defining and applying functions. According to MacTutor, it became “an invaluable tool for computer scientists,” and Church set out its mature form in his 1941 monograph The Calculi of Lambda-Conversion. The same system underlies the design of functional programming languages.
In 1936 Church published “A note on the Entscheidungsproblem,” in which he proved that there is no general algorithm to decide whether an arbitrary statement of first-order logic is provable. Alan Turing reached the same conclusion independently and by a different route the same year. The combination of their work is now known as the Church-Turing thesis: every effective computation can be carried out by a Turing machine, equivalently by Church’s recursive or lambda-definable functions.
Church supervised 31 doctoral students, including Alan Turing, Stephen Kleene, John Kemeny, William Boone, and Raymond Smullyan. Through these students and his own results, his influence runs through logic, the theory of computability, and the foundations of computer science.