Conel Hugh O’Donel Alexander, Irish-born British cryptanalyst, chess player, and chess writer, is born in Cork, County Cork, on April 19, 1909. He works on the German Enigma machine at Bletchley Park during World War II, and is later the head of the cryptanalysis division at Government Communications Headquarters (GCHQ) for over 20 years. In chess, he twice wins the British Chess Championship and earns the title of International Master. He is usually referred to as C.H.O’D. Alexander in print and Hugh in person.

Alexander is born into an Anglo-Irish family, the eldest child of Conel William Long Alexander, an engineering professor at University College Cork (UCC), and Hilda Barbara Bennett. His father dies during the Irish War of Independence in 1920, and the family moves to Birmingham in England where he attends King Edward’s School. He wins a scholarship to study mathematics at King’s College, Cambridge, in 1928, graduating with a first in 1931. He represents the University of Cambridge in the Varsity chess matches of 1929, 1930, 1931 and 1932.

From 1932, Alexander teaches mathematics in Winchester and marries Enid Constance Crichton Neate on December 22, 1934. In 1938 he leaves teaching and becomes head of research at the John Lewis Partnership.

In February 1940 Alexander arrives at Bletchley Park, the British codebreaking centre during the World War II. He joins Hut 6, the section tasked with breaking German Army and Air Force Enigma messages. In 1941, he transfers to Hut 8, the corresponding hut working on Naval Enigma. He becomes deputy head of Hut 8 under Alan Turing and formally becomes the head of Hut 8 in November 1942. In October 1944, Alexander is transferred to work on the Japanese JN-25 code.

In mid-1946, Alexander joins GCHQ, which is the post-war successor organisation to the Government Code and Cypher School (GC&CS) at Bletchley Park. By 1949, he has been promoted to the head of “Section H” (cryptanalysis), a post he retains until his retirement in 1971.

Alexander is twice a winner of the British Chess Championship, in 1938 and 1956. He represents England in the Chess Olympiad six times, in 1933, 1935, 1937, 1939, 1954 and 1958. At the 1939 Olympiad in Buenos Aires, Argentina, Alexander has to leave part-way through the event, along with the rest of the English team, due to the declaration of World War II, as he is required at home for codebreaking duties. He is also the non-playing captain of England from 1964 to 1970. He is awarded the International Master title in 1950 and the International Master for Correspondence Chess title in 1970. He wins the Hastings International Chess Congress 1946/47 with the score 7½/9, a point ahead of Savielly Tartakower. His best tournament result may have been first equal Hastings 1953/54, where he goes undefeated and beats Soviet grandmasters David Bronstein and Alexander Tolush in individual games. He is also the chess columnist of The Sunday Times in the 1960s and 1970s.

Many knowledgeable chess people believe that Alexander had Grandmaster potential, had he been able to develop his chess abilities further. Many top players peak in their late twenties and early thirties, but for Alexander this stretch coincided with World War II, when high-level competitive opportunities were unavailable. After this, his professional responsibilities as a senior cryptanalyst limited his top-class appearances. He defeats Mikhail Botvinnik in one game of a team radio match against the Soviet Union in 1946, at a time when Botvinnik is probably the world’s top player. Alexander makes important theoretical contributions to the Dutch Defence and Petrov’s Defence.

Conel Hugh O’Donel Alexander dies on February 15, 1974, in Cheltenham, Gloucestershire, England.