Daniel Bryan (more often known as Dan) was born in Dunbell, Gowran, County Kilkenny in 1900. From 1916, he studied medicine for two years at the National University of Ireland. In November 1917 he joined the Irish Volunteers to fight against British rule in Ireland.
The Irish Free State was created in 1922. During the subsequent Irish Civil War Bryan opted to join the National Army (later known as the Irish Army). He was commissioned to the rank of Captain in September 1923. He would remain in the Irish Army until his retirement in 1955.
For much of his career he served with the Headquarters Staff, specialising on intelligence. In 1942 he succeeded Liam Archer as Director of G2; he exercised a decisive personal contribution towards the detection and arrest of German spies in Ireland, such as Hermann Görtz and Günther Schütz. Bryan remained head of G2 for the remainder of the War. He closely co-operated with Richard Hayes, Director of the National Library of Ireland, in the breaking of German codes.
In 1952 he was appointed Commandant of the Irish Military College.
In 1983, RTÉ made a dramatised television series ("Caught in a Free State") about German spies in Ireland during World War II. A character closely based on Dan Bryan - "Colonel Brian Dillon" - was played by the Irish actor John Kavanagh.
- Memoir of Colonel Daniel Bryan (1900–85), University College Dublin Archives
- Article in The Sunday Times (London)
- Sunday Business Post: "Hitler's strange bunch of spies"