Remus Lupin

Remus John Lupin, nicknamed Moony, first appears in Prisoner of Azkaban as the new Defence Against the Dark Arts professor. His students, except those belonging to the Slytherin house, hold him in extremely high regard and love his hands-on teaching style. During his tenure, he gives Harry private lessons in casting the Patronus Charm, to aid him in fighting off the Dementors flanking the Hogwarts grounds. Until the climax of Prisoner of Azkaban, Lupin believes Sirius is guilty of betraying James and Lily, and of killing Pettigrew. Upon discovering that Sirius is innocent, and that the very much alive Pettigrew is the traitor, he helps Sirius to explain the truth to Harry, Ron, and Hermione in the Shrieking Shack. However, Lupin has forgotten to take the Wolfsbane Potion and so reverts disastrously to beast form, retaining zero control of his actions. Sirius, in dog form, drives Lupin safely away from the others into the Forbidden Forest, where he wakes come the morning restored to his human body and mind. However, Snape, furious over Sirius's eventual escape and his resultant loss of the Order of Merlin promised to him by Cornelius Fudge, publicly reveals the nature of Lupin's lycanthropy. Anticipating a public outcry in response to the threat he himself agrees he poses for students, Lupin resigns from his post.

Long after resigning from his post, Lupin remains in the story as a friend to Harry. In Harry Potter and the Order of the Phoenix, Lupin joins the newly reformed Order of the Phoenix and is part of the advance guard which escorts Harry from the Dursley family home in the book's opening chapters. Lupin is rarely seen in Grimmauld Place as he is often away performing secret tasks for the Order. Later in the book, Harry sees his father bully a school aged Snape through Snape's memory. Lupin does not participate in said bullying and gives several small indications that he disapproves of James's behaviour. When Harry confronts Lupin about the scene he witnessed in the Pensieve, Lupin expresses regret at never having had the courage to tell his friends when they were "out of order". Later, Lupin participates in the battle at the Department of Mysteries where he duels and overpowers Lucius Malfoy. In Harry Potter and the Half-Blood Prince, it is revealed that it was Fenrir Greyback who bit Lupin when he was a child, thus turning him into a werewolf. Towards the climax of the book, Lupin is part of the defenders of Hogwarts when Death Eaters penetrate the school, and after Dumbledore's death, it is revealed that Nymphadora Tonks has fallen in love with Lupin, despite a thirteen-year age gap. He resists becoming involved with her because of the many risks posed by his lycanthropy, and insists that she deserves someone "young and whole".

However, by the opening of Harry Potter and the Deathly Hallows, it is revealed that Lupin and Tonks have married. Later in the book, Lupin informs Harry, Ron and Hermione that Tonks is pregnant. However, feeling ashamed that he has turned Tonks into an outcast and that his unborn child would have a high chance of inheriting lycanthropy, he plans to leave Tonks and his unborn child. This results in an intense argument between Lupin and Harry. Eventually, he recognises the truth in Harry's words and returns to his wife in time for the birth of his son, Teddy Lupin. Lupin remains active in the Order throughout the year. He is often heard providing the casualty reports section on the pirate radio station Potterwatch under the pseudonym of Romulus. Lupin commands a group of defenders on the school grounds during the Battle of Hogwarts. Both Lupin and Tonks die in combat, killed by Antonin Dolohov and Bellatrix, respectively. Rowling has since stated that she originally intended for both Lupin and Tonks to survive, but finally killed them off to compensate for the last-minute reprieve she gave to Arthur Weasley. He makes one last appearance when Harry activates the Resurrection Stone to bring forth his parents, Sirius, and Lupin to comfort him. Lupin expresses his regret that Teddy will never know his father, but says that he will know why he died: trying to make a world in which his son could live a better life.