This is an anglicized form of the Olde Gaelic name O' Riagain or O' Raogain. There were three main septs of this family in Ireland, each with separate origins. The first belonged to Counties Meath and Dublin and were one of the Four Tribes of Tara (Tara was the seat of the high kings of Ireland). The second sept descended from Riagan, nephew of Brian Boru, High King of Ireland, (1002 - 1014). They ruled in the ancient territory of Tuathmhumhan (Counties Clare, Limerick and Tipperary). The third sept resided in Carbery (South West Cork) and were kinsmen of the MacCarthy's. Fineen MacCarthy, writing in 1595, mention fifteen families living there. The Reagans emigrated to the U.S.A. before the Famine a distinguished descendant being Ronald Reagan. The first recorded spelling of the family name is shown to be that of Maurice O' Regan (Gaelic O' Riagain), which was dated Born circa 1125 wrote an account of the Norman Inavasion, during the reign of "High Kings of Ireland with Opposition", 1170. Surnames became necessary when governments introduced personal taxation. In England this was known as Poll Tax. Throughout the centuries, surnames in every country have continued to "develop" often leading to astonishing variants of the original spelling.