Mrs. O'Leary

Ms. O'Leary is Percy's hellhound.

History
Mrs. O'Leary was originally Quintus' (Daedalus'), and had been tamed by him. It must have been a big undertaking, and she is faithful to Quintus and seemed to like Percy a lot, as well as Tyson and Bekendorf, but seems to despise Clarisse. Despite her size, she acts like any regular dog, eating scraps of food, playing fetch and licking people.

After Quintus died, Mrs. O'Leary was left in Percy's care, and defended and saved him from many close encounters.

Mrs. O'Leary allows Percy to travel through shadows, and she digs Chiron out after he is buried in rocks at the battle of New York City.

Mrs. O'Leary gets along well with Cerberus.

Physical description
Mrs. O'Leary is a very large, very scary and described as a mastiff. Mortals see her as a large standard poodle, rather than an impossibly big dog.

Powers
Mrs. O'Leary can shadow travel, though it tires her. She is also rather strong and agile, and relitevely intelligent