Remus Lupin (Mooney)

Professor Remus Lupin (aka Mooney) is a Werewolf and former Defence Against the Dark Arts teacher of Hogwarts'. He is the one who taught Harry about the Patronus Charm.

Prisoner
Lupin first appears when on the Hogwarts' Express where he helps Ron Weasley and Hermione Granger save Harry from the Dementors. It is revealed that he does not like the moonlight.

He is then revealed to be the new and third Defence Against the Dark Arts teacher for Hogwarts', and teaches the students about Boggarts and how to repel them, with a simple charm called Riddikulus. He then teaches Harry how to cast the Patronus Charm to defend himself against the Dementors, which are looking for Sirius Black but like Harry's soul as well.

At the Shrieking Shack, it is revealed that Lupin is Sirius' friend and also a friend of James and Lily Potter. He and Sirius explain the truth, and they capture Wormtail. However, before they can hand him in, Lupin turns into a Werewolf and Wormtail escapes. Lupin, as a wolf, attacks Sirius, Harry and Co.

The next morning, Lupin resigns as he is too much of a threat, and tells Harry that they'll meet again.