Old White is the wolf god, the father of mortal wolves. His mate, Night Black, is the Goddess of wolves. Old White is a large white wolf, Night Black is described as the shadow you see standing behind him.
Wolves give his name when in doubt or in terrorising situations, much like Tortallans use Mithros' name when praying etc.
Daine came across them after helping her pack, the Long Lake Pack, in a time of distress. They acknowledged her and thanked her for the help she had given the wolves as she and her teacher, Numair, rode back to Corus in Tortall. She also communicated briefly with him, as well as the cat goddess Queen Claw, after fighting a Cold Fang in Dunlath Castle.