Ontus Vanin is an imperial battlemage and retired member of the Mages Guild. He was with the guild for 40 years but says he’s useless and proud of it. Ontus openly admits to sleeping late and reading trashy books. When asked he’ll tell you the location of the deadric shrines for Hircine, Mephala, and Vaermina.
After the Thieves Guild steals Hrormir's Ice staff to get Hieronymus Lex out of the Waterfront as a sign of good faith they return the staff by leaving it in Ontus house since it’s too dangerous for them to return it directly to the Mages Guild.