Thomas Hamar Greenwood, 1st Viscount Greenwood, PC, KC (7 February 1870 – 10 September 1948), known as Sir Hamar Greenwood, Bt, between 1915 and 1929, was a Canadian-born British lawyer and politician. He served as the last Chief Secretary for Ireland between 1920 and 1922 and is associated with the activities of the Black and Tans in Ireland. Both his sons died unmarried meaning that the title of Viscount Greenwood became extinct in 2003.