The Tuatha Dé Danann are the children of the goddess Danu. Their very name, Tuatha Dé Danann, means "the people of Danu". However, who is their father?
There is this reference in Wikipedia:
The Tuatha Dé Danann were descended from Nemed, leader of a previous wave of inhabitants of Ireland.
Nemed -> Iarbonel -> Bethach -> Ibath -> Baath
The Nemedians were washed off of Ireland by a tidal wave raised by the Fomorians; some of the survivors
Ibath and his son Baath went into the north of the world
Baath -> Enda -> Tavarn -> Tat-> Aldui -> Ordam -> Etarlam -> Echtach -> Nuadu Airgetlam
Well after the disaster the Fir Bolg resettled Ireland. But then the Tuatha De Danann returned from the north and at the first battle of Mag Tuired
The pleasant Tuatha De Danann brought spears with them in their hands: With them Eochu was slain, by the seed of Nemed of strong judgement. Yet the Tuatha De Danann suffered great loss in the battle, and they left the king on the field, with his arm cut from him; the leeches were seven years healing him.
Nuadu Airgetlam was king over the Tuatha De Danann for seven years before their coming into Ireland, until his arm was hewn from him in the first battle of Mag Tuired.