The leader of a short-lived settlement in ancient Ireland, Neimheadh (sometimes written Nemed) arrived in Ireland about thirty years after the Partholonians were wiped out by a plague. The word Neimheadh was later used to refer to a place which was sanctified or held special meaning to the druids, and as such Neimheadh is often depicted as a powerful magician.
Neimheadh was originally part of a large fleet, but in their travels they encountered a small island whose only feature was a tower gilt with shining gold. Greed compelled them to attempt to seize the tower, but a great storm arose and scattered all the ships of the fleet. When the storm cleared, Neimheadh and those on his ship found themselves lost and alone in uncharted territory. They wandered aimlessly for over a year before happening upon the shores of Ireland.
The Partholonians all being dead, Ireland was once again under the control of the Fomorians. The Fomorians are most often depicted as demons living under the sea, but some accounts of what transpired between them and Neimheadh portray them instead as mere pirates. Interestingly, Dr. Daithi O hOgain, in his encyclopedia of Irish folk history, theorizes that this change stemmed from language issues: "Their designation.. meant 'underworld phantoms', but from a confusion of the element 'mór' (phantom) with 'muir' (sea) they came to be regarded as sea-pirates."
Regardless, three battles were fought between them in which Neimheadh triumphed due to his great skill in magic. As it was customary for the loser of a battle to pay tribute to the victor, the Fomorians sent their three best artisans to construct a stronghold for Neimheadh. They built for him the fortress of Rath Chinneich in what is now southern Armagh, after which he murdered them all to prevent them from going back and building a better one for the Fomorians. He died not long after - some sources say he was struck with a disease which made him decrepit (perhaps leprosy), while others attribute it to Fomorian revenge. Whatever the case, he was then buried on the island of Ard Neimhidh (now the Great Island in Cork harbor), which means approximately "highest of holy places".
With Neimheadh out of the way, the Fomorians returned and subjugated his descendants, exacting steep tributes from them as vengeance for his deeds. After enduring as much as they could, Neimheadh's people rose up against the Fomorians and assaulted their stronghold of Tor Inis (literally, "island tower"). During this battle, the Fomorian king Conan was killed and the Nemedians captured the tower. Conan's brother Morrig ("great king") returned immediately after from a journey and drove the battle-weary Nemedians from Ireland.
From one of Neimhead's grandsons, Semeon, the race known as the Fir Bolg were descended. Some folk historians also claim that another of his grandsons, Briotan Mhaol, fled to what is now England where he fathered the race of the Britons.