This name, with variant spelling MacGenis, McGinnis, MaGennis, Guin(n)ess etc., is an anglicized form of the Olde Gaelic (Scots and Irish) 'MagAonghusa'. The Gaelic prefix 'mac' (frequently written as 'mag' before a vowel) indicates 'son of'. Aonghusa is the genitive form of the male given name Aonghus meaning 'Unique Choice' from 'aon', one plus 'gus', choice or enterprise. The first bearer of the name is believed to be Aonghus Turimleach, one of three Irish brothers, who invaded Scotland in the 3rd Century B.C., and gave his name to the district of Angus. The ancestry of the Gaelic Irish McGuinness family goes back to a 5th Century chief of Dal Araidhe. By the 12th Century they had become territorial lords of Iveagh in County Down and their fortress was at Rathfriland. Several of the clan fought with Hugh O' Neill at the victorious battle of the Yellow Ford in 1598. The present Lord Iveagh, is head of the largest brewery concern in the world - Guinness of Dublin, which was set up by Arthur Guinness in 1759. The first recorded spelling of the family name is shown to be that of Mag Aonghusa, which was dated circa 1150, in "Early Records of Iveagh", County Down, during the reign of Turlough Mor O' Connor, High King of Ireland, 1119 - 1156. 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.