This paper traces the career of Peter B. Denes (1920–1996). Born in Hungary, he migrated to Britain at the age of 18 and qualified as an electrical engineer. He became a naturalised British subject and was recruited as a lecturer to the Phonetics Department at University College London, playing a major part in the teaching and research of the department throughout the 1950s. With his colleague Dennis Fry he designed an automatic speech recogniser which was the first to operate with an unlimited vocabulary and to make use of a store of linguistic knowledge. In 1961 he moved to Bell Laboratories in the USA and soon became Head of the Speech and Communication Research Department there. At Bell Labs he was influential in championing the use of dedicated laboratory computers for speech research. Seen in retrospect, his long career casts light on numerous facets of speech research in the second half of the twentieth century.