Sir Charles Antony Richard Hoare, known to colleagues as Tony, died on 5 March 2026, aged 92. Over six decades, the British computer scientist made foundational contributions to programming languages, algorithms, operating systems, formal verification, and concurrent computing.
Hoare developed the Quicksort algorithm in 1959 while working on a machine translation project for which he needed to sort Russian dictionary words into alphabetical order before they could be looked up on magnetic tape. The story of how the algorithm came to be implemented became legendary in computing circles. He told his boss at Elliott Brothers Ltd that he knew a faster sorting algorithm than the one the company had just implemented. His boss bet him sixpence that he did not. Quicksort was faster.
The bet may have been informal, but its consequences were vast. Quicksort gained widespread adoption, appearing as the default library sort subroutine in Unix and lending its name to the C standard library subroutine qsort and the reference implementation of Java. More than six decades later, it remains among the fastest sorting methods available, particularly for randomly ordered data.
Yet Quicksort was only the beginning of Hoare's influence on computing. His development of Communicating Sequential Processes revolutionised how we understand concurrency by treating independent processes as entities that communicate through synchronised exchanges, providing a framework for the parallel computing world we inhabit today. His 1980 Turing Award lecture, "The Emperor's Old Clothes," remains required reading for system designers, famously warning against the traps of needless complexity.
Hoare lived long enough to witness the consequences of one decision he came to deeply regret. He famously called the null reference, which he invented, a "billion-dollar mistake", a term he had popularised in a 2009 talk. That decision led to decades of NullPointerExceptions in Java, segmentation faults in C, "cannot read property of undefined" in JavaScript, and countless debugging hours tracking down null pointer errors. Yet there was an unexpected benefit to his public confession. Modern languages designed after his 2009 talk prioritised null safety in ways earlier languages never did. Rust eliminated raw null entirely. The pattern is clear: languages learned from Hoare's mistake.
Hoare married Jill Pym in 1962, and they had three children. He became Professor of Computing Science at Queen's University of Belfast in 1968 and returned to Oxford in 1977 as Professor of Computing to lead the Programming Research Group, where much of his foundational work on formal verification took shape.
By all accounts, Hoare was warm and humble, and remained intellectually sharp well into old age. One colleague recalls visiting him repeatedly and finding a man who could recount career stories with pinpoint clarity and who expressed scepticism about Hollywood's portrayal of genius.
The computer science community recognised his contributions early. Hoare received the Turing Award in 1980 for fundamental contributions to programming language definition and design, with the award presented at the ACM Annual Conference in Nashville, Tennessee, on 27 October 1980.
His death marks the end of an era that saw computing emerge from room-filling machines to something that shapes nearly every aspect of modern life. Yet his ideas remain embedded in the systems millions of people use every day.