The Fat Friar
House: Hufflepuff ghost
Distinguishing Characteristics: A diminutive and rotund ghost in a monk's garb.
First Mention: Sorcerer's Stone/Philosopher's Stone, chapter seven
General: The Friar is as friendly and forgiving as a representative of Hufflepuff House should be. No one pretends he can control Peeves, but he's the only one who seems to see any potential good in him. At the beginning of each Hogwarts year, the Fat Friar argues (to no avail) Peeves' case that he should accompany the other ghosts to the start-of-year feast.
Unlike the mysterious Grey Lady of Ravenclaw and the frightening Bloody Baron in Slytherin, The Fat Friar is friendly with students, conversing regularly with them. He provides Harry and the other first years with their first friendly greeting within Hogwarts Castle in SS/PS. He keeps Ernie Macmillan (and through him, other students) informed about Umbridge's problems as headmistress in Order of the Phoenix. He is clearly an ally to Harry and his friends, and could also be a source of information in the future.