Alonzo Church (June 14, 1903 – August 11, 1995) was an American mathematician and logician who made major contributions to mathematical logic and the foundations of theoretical computer science. He is best known for the lambda calculus, Church's thesis and the Church-Rosser theorem.
Alonzo Church was born on June 14, 1903 in Washington, DC where his father, Samuel Robbins Church, was the Justice of the Municipal Court for the District of Columbia. The family later moved to Virginia after his father lost this position because of failing eyesight. With help from his uncle, Alonzo Church was able to attend Ridgefield High School in Connecticut. After graduating from Ridgefield in 1920, Church attended Princeton University where he was an exceptional student, publishing his first paper, on Lorentz transformation, and graduating in 1924 with a degree in mathematics. He stayed on at Princeton, earning a Ph.D. in mathematics in three years under Oswald Veblen.
He married Mary Julia Kuczinski in 1925 and the couple had three children, Alonzo Church, Jr. (1929), Mary Ann (1933) and Mildred (1938).
After receiving his Ph.D. he taught briefly as an instructor at the University of Chicago and then received a two-year National Research Fellowship. This allowed him to attend Harvard University in 1927-28 and then both University of Göttingen and University of Amsterdam the following year. He taught at Princeton, 1929–1967, and at the University of California, Los Angeles, 1967–1990.
He died in 1995 and was buried in Princeton Cemetery.
The lambda calculus emerged in his famous 1936 paper showing the existence of an "undecidable problem". This result preceded 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." This resulted in the Church-Turing thesis.