This notable and long-established surname, widespread in the Irish provinces of Munster and Leinster, is ultimately believed to be of Welsh origin, introduced into Ireland in the wake of the Anglo-Norman Invasion of 1169 - 1170, led by Strongbow, a Norman living in south Wales. The derivation is from the Old Welsh personal name "Cadwgan", a diminutive of the Celtic element reflected in the Welsh "cad", battle, or else a pet form of "Cadfael, Cadog", from "cad", battle, and "mael", prince. The Earls Cadogan are said to be descended from Cadwgan, prince, and ruler of south Wales, who died in the year 1112. William Cadogan (1675 - 1726), created first Earl Cadogan (1718), was born in Dublin, and Major William Cadogan was appointed governor of Trim in 1649. The County Cork family of Cadogan are said to be native Irish in origin, but the Gaelic form of their name, "O'Ceadagain", is also likely to be a version of the Welsh "Cadwgan", as its Gaelic etymology is uncertain. It has been suggested by Fr. Woulfe, and later by MacLysaght, leading authorities on Irish surnames, that "O'Ceadagain" translates as "one possessing hundreds", from "cead", a hundred, or else that the root word is "cet", a blow or buffet, but neither of these derivations have been proven. In 1341, Thomas and Bartholomew Cadigan, noted in the Gormanston Register, were considerable landholders in County Limerick, their place being called Martyncadyganestown. The first recorded spelling of the family name is shown to be that of Cadivor Cadigan, which was dated 1292, in the "Subsidy Rolls of Monmouthshire", Wales, during the reign of King Edward 1, known as "The Hammer of the Scots", 1272 - 1307. 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.