Llywellyn m. Lugus, the name of a Celtic deity, deriving from Proto-Celtic *lug, of disputed meaning, + Belenus, the name of a Celtic sun deity, of uncertain origin, possibly relating to the god-name Apollo.
The name of a 10th C king of Powys, an 11th C king of Gwynedd, Powys, and Deheubarth, a 12th-13th C prince of Gwynedd, a 13th C prince of Gwynedd, a 13th C king of Wales, a 13th C prince of Gwynedd.
This name became increasingly popular in Wales after the reign of Llywelyn the Great in the 12th-13th C, so much so that when Shakespeare needed to name a generic Welsh captain in Henry V, he named him Fluellen, a roughly phonetic version of the English pronunciation of Llywellyn. From the 13th C on, Anglo-Norman scribes often equated the name with Lewis (cf. Louis).