Lugh was the son of Ethne, daughter of Balor, and Cian, son of Dian Cécht the Healer, a prince or chieftain of the Tuatha Dé Danann. It had been foretold that Balor could only die by the hand of his own grandson so, when Ethne gave birth to Lugh, Balor ordered the baby to be drowned. A stillborn infant was thrown into the sea instead and Lugh was fostered by Tailltu, daughter of the King of Spain and Queen of the Fir Bolg and later by the Shí of Mananann Mac Lir, the sea god.

When the Tuatha Dé Danann, under Nuada, were preparing secretly for war with the Fomor Lugh arrived with a Fairy host and demanded entrance to the royal fortress at Tara. The guard did not recognise either the hero or his name so he called to the Il-Dána to identify himself and name his skills. For each of the skills - warrior, harper, poet, historian, hero, sorcerer etc - that Lugh named there was already a practised master within the palace; but at last Lugh told the door keeper to go and ask Nuada if he knew of any one man who possessed all these arts. When Nuada heard of Lugh's coming he said:
"Let him come in, for never before has his like entered this fortress."

The doorkeeper returned to Lugh and, curious, asked him which arts he counted as the greatest. Lugh replied:
"Swimming forever without tiring, Carrying a cauldron with both elbows Outrunning the swiftest of horses Leaping on a bubble without breaking it."

Then the doorkeeper bade him enter and went to open the fortress gates but Lugh prevented him saying:
"Do not open the gates now for the sun has set and it is unlucky to unlock them till dawn."

Then Lugh took three steps back and with one great leap cleared the fortress wall of Royal Tara and took his place at the Scholar's Seat among the warriors of the Tuatha Dé Danann.

The Tuatha Dé fearing an early death for Lugh, precious as he was "owing to the multitude of his arts, " decided to prevent him from entering the fray at Moy Tura too soon, but he escaped from his guardians and appeared in the vanguard of the warriors of the tuatha exhorting them to fight, moving like the wind through the ranks "on one foot, and with one eye" chanting his battle-song to lend them strength and courage.

He thus assumed the characteristic posture of a sorcerer mimicking the monstrous form that tradition has ascribed to the Fomor.