Ira Rosenberg's favorit daughter nailing up crusifixes. I think it was season two after malaikat went to the dark side but I can't remember the episode.
I don't think we ever hear what his name is, just that he's Willow's dad. Though according to buffy.wikia.com/wiki/willow_rosenburg it says her father's name is Ira, but I don't recall ever hearing his name come up.