Lludd Llaw Ereint
: HLIÐ HLAW EH-raynt (or HLÜÐ) (ð=th as in leather)
Welsh: Obstacle Silver-Hand
Legendary King of Britain, ca. the time of Christ or just before, also called Lud in the Latin texts (History of the Kings of Britain). He is said to have refortified the walls of Tri Novantum, and for that the city was renamed Caer Lludd, or Londres, which in modern Welsh is Lundein--London. Of course, this is nonsense--it's the Romans that called it Londinium, and it was never called Tri Novantum ("New Troy" from the legend that the Britons--Cymry--are decended of the Trojans).
The son of Don and Beli Mawr, he gained the crown presumably after his brother Caswallawn (who stole it from the Children of Llyr) died. Under his reign, three plagues infected his land--the Corianid (a race of fairy), fighting dragons, and an invisible man who invaded his hall, not unlike Grendel. With the help of his brother Llefelys, he is able to defeat all three.
According to Geoffrey, Lludd quarreled with Nynniaw about renaming the city in his honor (Nynniaw/Nennius wanted to keep the name Trinovantum), but doesn't say how it ended. (I can't find a copy of Gildas right now; when I do, I'll tell you what he said about it]).
Lludd is said to be buried at Ludgate in London; his father Beli Mawr is at Billingsgate, just as Bran is at Tower of London.
As a god, Lludd is usually equated with Nudd, due to the similarity of name, and Lludd's name "Silver-Hand," which corresponds with the Irish god Nuada, who is equivalent to Nudd. Nudd is considered a war god, as is Nuada. Sometimes, Lludd is equated with Lugh Lamhada (Lugh of the Long Arm), based on similarity of name, though not of attribute.
Personally, I hold that Lludd is a confluence of the gods Nudd and Llyr. My reasoning is beacause of two figures who are said to be the son and daughter of Lludd. The first is Creiddylad/Cordelia, said sometimes to be the daughter of Lludd, sometimes of Llyr/Lear. The second is Manannan/Manawyddan, in Irish called both the son of Lir/Llyr and of Alloid/Lludd.