Sir Charles Antony Richard Hoare ( ; 11 January 1934 â 5 March 2026), known as Tony Hoare or C. A. R. Hoare, was a British computer scientist who made foundational contributions to programming languages, algorithms, operating systems, formal verification, and concurrent computing. His work earned him the 1980 ACM Turing Award, usually regarded as the highest distinction in computer science.
Hoare developed the sorting algorithm quicksort in 1959âÂÂ1960. He developed Hoare logic, an axiomatic basis for verifying program correctness. In the semantics of concurrency, he introduced the formal language communicating sequential processes (CSP) to specify the interactions of concurrent processes, and along with Edsger Dijkstra, formulated the dining philosophers problem. From 1977 on, he held positions at the University of Oxford as well as at Microsoft Research in Cambridge.
Tony Hoare was born in Colombo, Ceylon (now Sri Lanka) on 11 January 1934, to British parents; his father was a colonial civil servant and his mother was the daughter of a tea planter. Hoare was educated in England at the Dragon School in Oxford and the King's School in Canterbury. He then studied Classics and Philosophy ("Greats") at Merton College, Oxford. On graduating in 1956 he did 18 months National Service in the Royal Navy, where he learned Russian. He returned to the University of Oxford in 1958 to study for a postgraduate certificate in statistics, and it was here that he began computer programming, having been taught Autocode on the Ferranti Mercury by Leslie Fox. He then went to Moscow State University as a British Council exchange student, where he studied machine translation under Andrey Kolmogorov.
In 1960, Hoare left the Soviet Union and began working at Elliott Brothers Ltd, a small computer manufacturing firm located in London. There, he implemented a compiler for the language ALGOL 60 and began developing major algorithms.
Hoare was involved with developing international standards in programming and informatics, as a member of the International Federation for Information Processing (IFIP) Working Group 2.1 on Algorithmic Languages and Calculi, which specified, maintains, and supports the languages ALGOL 60 and ALGOL 68.
Hoare became the Professor of Computing Science at the Queen's University of Belfast in 1968, and in 1977 returned to Oxford as the Professor of Computing to lead the Programming Research Group in the Oxford University Computing Laboratory (now Department of Computer Science, University of Oxford), following the death of Christopher Strachey. He became the first Christopher Strachey Professor of Computing on its establishment in 1988 until his retirement at Oxford in 2000. He was an Emeritus Professor there, and also a principal researcher at Microsoft Research in Cambridge, England.
Hoare's most significant work has been in the following areas: his sorting and selection algorithm (Quicksort and Quickselect), Hoare logic, the formal language communicating sequential processes (CSP) used to specify the interactions between concurrent processes (and implemented in various programming languages such as occam), structuring computer operating systems using the monitor concept, and the axiomatic specification of programming languages.
Speaking at a software conference in 2009, Hoare apologized for inventing the null reference:
For many years under his leadership, Hoare's Oxford department worked on formal specification languages such as CSP and the Z notation. These did not achieve the expected take-up by industry, and in 1995, Hoare was led to reflect upon the original assumptions:
A commemorative article of reminiscences was written in tribute to Hoare for his 90th birthday.
In 1962, Hoare married Jill Pym, a member of his research team, with whom he had three children. He died on 5 March 2026, aged 92.