Conel Hugh O'Donel Alexander
Conel Hugh O'Donel Alexander (19 April 1909 – 15 February 1974), known as Hugh Alexander and C. H. O'D. Alexander, was an Irish-born British cryptanalyst, chess player, and chess writer. He worked on the German Enigma machine at Bletchley Park during the Second World War, and was later the head of the cryptanalysis division at GCHQ for 25 years.
Source: Wikipedia — Conel Hugh O'Donel Alexander (CC BY-SA 4.0)