"[1] Daniel Bryan (more often known as Dan) was born in Dunbell, Gowran, County Kilkenny in 1900.
In 1940 when a cipher was found on the first German agent to be captured in Ireland, Wilhelm Preetz, Bryan recruited Richard J. Hayes Director of the National Library of Ireland as a codebreaker and closely co-operated with him in the breaking of German codes.
[2] 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.
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.