"Gallghad"?
Where did you come across that?
The origin of the name is not known. It's presumed to be of Celtic origin, some suggesting links with the Welsh "cad" (battle) or "gwalch"(hawk).
Others think that its origins lie in the Biblical name Gilead.
In "Lorgaireacht an tSoidhigh Naomhtha"
http://www.celt.dias.ie/publications/cat/f/f2-6.html he's named "Galafas".