he Ryans are decended from a 2nd century King of Leinster, Cathaoir Mór. The meaning of the name remains uncertain, but it may mean illustrious. The Irish version of the name, Ó Maoilriain, from the main Ryan sept, is now usually abbreviated to Ó Riain, the name of the small Leinster sept of the Ryans. Other anglicised versions of the name include Mulryan in Co. Tipperary and O'Ryan in Co. Carlow.

Among the holder of the name were Cornelius Ryan (1920-1974), born in Synge Street, Dublin, who became a war correspondent during World War II and subsequently wrote The Longest Day, about the D-Day landings in 1944. In sports, Ken Ryan has been secretary-general of the Olympic Council of Ireland since 1976, while Paddy Ryan (born in Pallasgreen, Co. Limerick in 1883), emigrated to the United States where he became an Olympic hammer thrower for his adopted country.