Where does “Llewelyn” come from?

Llewelyn is an English adoption of the Welsh name Llywelyn, which derives from Proto-Brythonic Lluɣβelen, ultimately from Proto-Celtic Lugus.

Ancestry of “Llewelyn”, step by step

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