Ard-Greimne is mentioned in the last book.
The only thing they say about him is that he is the father of Scathath and Aoife. He also pushes Aten into the volcano Tarturus.
Ard-Greimne is A supposed Dark Elder, due to the fact that he orders anpu to fire screaming arrows into a crowd of Humani. He is in league with Anubis and Bastet and Dagon.