The family name Regan, along with its cognates O'Regan, O Regan, Reagan, and O'Reagan, is an Anglicized form of the Irish surname Ó Riagáin or Ó Ríogáin, from Ua Riagáin. The meaning is likely to have originated in ancient Gaelic ri "sovereign, king" and the diminutive suffix -in; thus "the king's child" or "big king". The name was borne by two distinct families: one seated in Meath, the other in Thomond. The O'Regans of Meath were a branch of the southern Ui Neill and one of the four Tribes of Tara. Before the Anglo-Norman invasion, they were lords of south Breagh and the north of present-day County Dublin. They took a leading part in the wars against the Danes. In the year 1029, Mathghamhain Ó Riagáin, king of Breagh, captured the king of Dublin, Amhlaoibh son of Sitric, releasing him only upon payment of an enormous ransom, which included the celebrated Sword of Carlus. The O'Regans were dispossessed soon after the invasion and dispersed through Ireland. The O'Regans of Thomond are a Dalcassian family said to be descended from Riagán, son of Donncuan, brother of Brian Boru, and now numerous throughout Ireland. The unisex forename Regan is likely to have derived sometime later from the Latin Regina "queen", the feminine form of Rex (stem reg-) "king", which is also the source of the name Reginald. Persons with the surname Bill Regan (disambiguation) Bob Regan (born 1947), American country music songwriter Brian Regan (disambiguation), several people Bridget Regan (born 1982), American actress Charles Tate Regan (1878–1943), British ichthyologist Daithí Regan (born 1968), Irish hurler David M. Regan (born 1935), Canadian psychologist Donald Regan (1918–2003), U.S. Treasury Secretary and Chief of Staff to President Ronald Reagan Edward Regan (1930–2014), American politician and government bureaucrat Eugene Regan (born 1952), Irish barrister and politician Fionn Regan (born 1981), Irish folk musician Frank S. Regan (1862–1944), American politician and businessman Geoff Regan (born 1959), Canadian politician and federal cabinet minister, son of Gerald Regan Gerald Regan (1928–2019), 19th premier of Nova Scotia, father of Geoff, Laura and Nancy Regan Jack Regan (1912–1988), Australian rules footballer James Regan (disambiguation) Jayne Regan (1909–2000), American actress Jessica Regan (born 1982), Irish actress Joan Regan (1928–2013), English singer John Regan (disambiguation) Judith Regan (born 1953), book publisher Julianne Regan (born 1962), English singer, songwriter and musician, lead singer of the band All About Eve Kelly Regan (born 1961), Canadian