Thomas Ulick Sadleir (15 September 1882 – 21 December 1957) was an Irish genealogist and heraldic expert.
In 1915 he was appointed registrar of the Order of St Patrick by George Dames Burtchaell, Deputy Ulster King of Arms.
[2][3] In August 1921, Burtchaell was killed in a tram accident, and in September, Sadleir was appointed Deputy to Major Sir Neville Wilkinson, Ulster King of Arms.
The Office of Arms was unaffected by the creation of the Irish Free State in December 1922, continuing to cover the whole of the island of Ireland, and remaining based in Dublin Castle.
He maintained links with his former employer, however, remaining a trustee of the Heraldic Museum in Dublin until his death.