Ontus Vanin is a retired Imperial who is said to have spent 40 years in the Arcane University.
He mentions that he likes to "sleep late and read trashy books". He also apparently "cares nothing about the Mages Guild", although he is a former member of it. He also wears White Mage's Robes.
Ontus lives in the Talos Plaza District, with his hidden treasures. He plays an important part in the Thieves Guild mission, Misdirection.