is the spiritual and temporal leader of the people of Series Eleven
His official title is "High Father of the Sept", and he is thousands of years old, having kept himself alive and well by occasionally consuming the souls of his subjects, which all belong to him by law. He is the equivalent of the Chrestomanci of Series Eleven.
He is tall and bulky, and has white hair and a white beard. He wears lion skins and many ornaments.
He is absolutely selfish, accustomed to doing whatever he wants.
It is said that he is responsible for keeping Series Eleven down to a single world, in order that he have no rivals.
See also The Lives of Christopher Chant (spoilers).