He is the regent of Robert Arryn ( A 6 year old boy who is The Lord Paramount of The Vale).
Lord Nestor Royce is the junior member of House Royce and Keeper of the Gates of the Moon. He has been High Steward of the Vale for the fourteen years prior to Lord Jon Arryn's death.
Nestor is a massive, barrel-chested man. He is bald and wears a greying beard.