Who is Oldpappy Guester from Seventh Son and what is their importance?

Oldpappy Guester is Peggy's grandfather on her father's side. He encourages Peggy and jokes with her whenever he gets the chance. He seems to have learned from his mistakes because he says he hit Horace with the hazel rod too much as a child, so now Horace is too quick to use the rod on little Peggy. He wants Peggy to understand that her knack as a torch does not make her wicked but makes her special.