Was King Arthur Irish? After four years of research and the translation of ancient Irish manuscripts the forgotten story of the Irish Arthur can now be introduced and revealed for the first time in hundreds of years. From long forgotten manuscripts this scholarly paper has pieced together a tale that will astound those seeking the origins of King Arthur. Most of this material has never been seen or read before, with much of it newly translated into English for the first time, both narrative prose and ancient poetry. The main sources are discussed first and then the implications of the ancestry, name and background of this fascinating character of Irish history and myth are examined. What then unfolds is a tale of astounding similarities to that of the Arthur of the Welsh. With over two hundred footnotes there is plenty of information for those seeking further clues and answers to the enigma and origins of King Arthur.