The family name Regan, and its cognates O'Regan, O Regan, Reagan, O'Reagan, is an Anglicized form of the Irish surname Ó Riagáin or Ó Ríogáin, from Ua Riagáin. The meaning is likely to originate in ancient gaelic from ri "sovereign, king" and the diminutive -in, "the king's child", transliterating as "little king".
