Newgrange was, in the early stories, known as Síd in Broga and Brug na Bóinne. It later became known as Brug Mac Ind Óc after its owner, Dagda, the chief of the Tuatha Dé Danann, was tricked out of ownership by his son.
The oldest name of Newgrange, according to the manuscripts, was Síd in Broga. But it later became known as Brug Maic Ind Óc after a curious incident in which The Dagda, the chief of the gods, was deprived of his most precious palace by his son, Oengus Óg. An early text, De Gabáil int Síde, the Taking of the Síd, tells how Dagda distributed the various síd or monuments to the Dé Dananns. Oengus Óg was in foster care at Brí Leith with Midir, having been born of an illicit union between the Dagda and Bóinn, wife of Elcmar. Newgrange/Síd in Broga was said to have been built by the Dagda himself:
Behold the síd before your eyes,
It is manifest to you that it is a king's mansion
Which was built by the firm Dagda;
It was a wonder, a court, an admirable hill.
J.A MacCulloch, in Celtic Mythology (1918), takes up the story:
This was the Brug na Bóinne. Oengus Mac Ind Óc, or "Son of the Young Ones," viz. Dagda and Boann, was then with his foster-father Midir, but soon claimed his abode as Esau did his blessing. The claim, however, could not be granted, whereupon Oengus asked to spend the night in Dagda's palace, to which his father agreed, granting him also the next day. When this had elapsed, Oengus was bidden to go, but refused, because, time being composed of day and night, his tenancy must be perpetual. Thus Dagda was dispossessed; and the síd, passing to Oengus, took his name, Brug Maic Ind Óc.