This interesting surname is Irish. It derives from O' Riagain, composed of the elements O', meaning male descendant of, and the personal name Riagan, from "riodhgach", meaning impulsive. This is a widespread name which came, not from one ancestor, but from several. There were O' Riagains in Meath and Dublin, who were important because they were of the "Four Tribes of Tara". These were very active against the Scandinavian invadersohe 10th century, but lost their importance with the arrival of the Normans in 1180, who drove them away to Leix. Another, and in no way related sept, were descended from one of Brian Boru's brothers, Donnchadh. They were all of the powerful Dalcassian sept which ruled in Counties Clare and Tipperary, and all of Leinster. Another sept, living in Carbery, claim to be akin to the McCarthys. In the modern idiom the surname has several spellings including Regan, Reagan, O'Regan and O'Reagan. The first recorded namebearer (see below) wrote a history concerning the arrival of the Normans in the 12th Century. As a kind of diplomatic secretary to Dermot McMurrough, King of Leinster, he was well positioned to give a first hand account. Teige O'Regan (born 1620) was a faithful follower of James 11. He greatly distinguished himself at the siege of Claremont and Sligo. The Coat of Arms granted to the family is a gold shield with an ermine chevron between three blue dolphins. The first recorded spelling of the family name is shown to be that of Maurice O'Regan, which was dated 1125, in the Records of Leinster, Ireland, during the reign of Turlough Mar O'Connor, High King of Ireland, 119 0 - 1156.