Julius Richard Büchi (1924–1984) was a Swiss logician and mathematician.
He received his Dr. sc. nat. in 1950 at the ETH Zürich under supervision of Paul Bernays and Ferdinand Gonseth. Shortly afterwards he went to Purdue University, Lafayette, Indiana. He and his first student Lawrence Landweber had a major influence on the development of theoretical computer science.
Together with his friend Saunders Mac Lane, a student of Paul Bernays as well, Büchi published numerous celebrated works. He invented what is now known as the Büchi automaton, a finite state automaton accepting certain collections of infinite words known as omega-regular languages. The "n squares' problem", known also as Büchi's problem, is an open problem from number theory, closely related to Hilbert's tenth problem. One of his students was Lawrence Landweber who received his doctorate at Purdue University in 1967.
- Finite Automata, Their Algebras and Grammars -- Towards a Theory of Formal Expressions. Published posthumously, Springer, New York 1989.
- Collected Papers of J. Richard Büchi. Edited by Saunders Mac Lane and Dirk Siefkes. Springer, New York 1990.