Where does “Llewellyn” come from?

Llewellyn is an English adoption of Welsh Llywelyn, from Proto-Brythonic Lluɣβelen, derived from Proto-Celtic Lugus.

Ancestry of “Llewellyn”, step by step

Step	Language	Word	Meaning
1	Welsh	Llywelyn	—
2	Proto-Brythonic	Lluɣβelen	—
3	Proto-Celtic	Lugus	the god {{w\|Lugus}}