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–Turing thesis, proving the unsolvability of the Entscheidungsproblem ("decision problem"), Frege–Church ontology, and the Church–Rosser theorem. He also worked on the philosophy of language. Alongside Alan Turing, Church has been considered one of the founders of computer science.