The great and illustrious Irish family of O' Sullivan descend from Eoghan Mor, father of the famous Olioll Olum, 3rd Century King of Munster. The Mac Carthy's, O'Keeffes and O'Callaghans were the other leading families of the Munster Eoghanacht i.e., descended from the above mentioned Eoghan, but (O)Sullivan remains the most widespread surname in Munster. The surname is an anglicized form of the Gaelic "O'Suileabhan". The Gaelic prefix "O" indicates "male descendant of", plus the personal byname Suileabhan, variously interpreted as "hawk-eyed" or "one-eyed". Several members of the clan were lords of the territory near Cahir, (Co. Tipperary), prior to the Anglo-Norman invasion. From 1200 on, they spread to Counties Cork and Kerry dividing into two main septs - O'Sullivan Mor and O'Sullivan Beare. The senior chieftain of the former sept had his stronghold at Kenmare Bay, Co. Kerry, and the latter chieftain was lord of Beare and Bantry. Owen Rua O'Suileabhan (1748-1784), was a great lyric poet, and Sir Arthur Sullivan, (1842-1900), of the Gilbert and Sullivan operas, was of Irish descent. The first recorded spelling of the family name is shown to be that of Donal O'Sullivan Beare, which was dated 1560-1618, hero of the Siege of Dunboy, recorded in "Records of Dunboy, Bantry Bay", during the reign of Queen Elizabeth 1st, known as "Good Queen Bess", 1558 - 1603. Throughout the centuries, surnames in every country have continued to "develop" often leading to astonishing variants of the original spelling.