Chapeau-jii

An old demon with the form of a hat, he possesses great knowledge in all the matters related to the underworld and demons. In the OVA, he is often sleeping because of his old age and is mostly in the head of Enma. While he rarely takes action, he advises Enma of the best course of action as well as alerting him of the presence of demons. In the manga, he is younger, can change of shape and appearance, has a more aggressive personality and a more active role
He also has a habit of using the sentence-ending copula "jaja"

(Source: Wikipedia)