Remus John Lupin is a character in the Harry Potter book series by J. K. Rowling. Warning! Spoilers from book 3-5 in this node!
Biography until year 1993
Remus Lupin was born in 1959. He is half-blood, meaning that one of his parents is either muggle or muggle-born. When he was a young child he was bitten by a werewolf and became a werewolf himself.
Wizards and witches are normally very afraid of werewolves, thus Lupin's parents thought he won't be accepted into Hogwarts schoold for witchcraft and wizardry by the headmaster then, Professor Dippet.
But there was hope for Lupin when Albus Dumbledore became headmaster. Dumbledore accepted Remus to Hogwarts, but took certain steps of precaution. He built the Shrieking Shack in the town of Hogsmead, and dug a tunnel into there from Hogwarts. On the enterance of the tunnel he planted the Womping Willow, a highly violent tree. According to the plan, every month, when Lupin will become a werewolf, he will go into the shrieking shack and stay there until he returns to his human form.
In September, 1970 Remus entered Hogwarts. In Hogwarts, Remus met three good friends: James Potter, Sirius Black and Peter Pettigrew. The four get into mischief, very much like Fred and George Weasley. Together they create the marauder's map.
All this time Lupin keeps the fact that he is a werewolf secret, even from his friends. But at last they find out about it. Remus thought that once they found out they will stop being friends with him, but instead they decided to become Animaguses - wizards who can turn into animals whenever they like.
At last, at their fifth year at Hogwarts, they achieved it. James could turn into a stag, Sirius into a dog, and Peter transformed to a rat. Every month, the four of them went to the shrieking shack under James's invisibility cloak, and in the shack transformed into animals. Werewolves are only dangerous to humans, so they were safe. James and Sirius turned into big enough animals to hold a werewolf down, and in this way they went out to nightly walkes on the Hogwarts grounds.
After graduating from Hogwarts, it was very difficult for Lupin to find a job, as most witches and wizards hate werewolves. In Voldemort's years of teror Lupin was a member of the Order of the Phoenix, a group of witches and wizards lead by Dumbledore who fought Voldemort and the Death Eaters (his followers).
In 1981 James Potter and his wife Lily were murdered by Voldemort. But when Voldemort came to murder their son, Harry, Harry was left only with a scar, and Voldemort went into hiding.
After Voldemort's defeat, the whole magical world was happy. The bad part was that they thought Sirius Black was a Death Eater. Sirius is sentenced for a lifetime in Azkaban, wizard prison.
At last, in 1993, Dumbledore hired Lupin as the new Defense Against the Dark Arts teacher at Hogwarts.
Events after 1993
In the summer of 1993, Sirius Black escaped from Azkaban. He was the first in to do so history. Obviously, all the wizards, even Lupin, thought he's after Harry. To keep Harry safe, Dementors, scary creatures who guard Azkaban prison, were placed at the enterances to Hogwarts.
At Hogwarts, Harry Potter is one of Lupin's students. Harry is startled to learn that Lupin used to be his dead father's friend.
In June 1994, Harry and Lupin meet Sirius Black. Sirius convinces them that the crimes he had been convicted for were actually preformed by Peter Pettigrew, their old friend, who had later become a Death Eater.
Professor Snape, one of the teachers at Hogwarts, tells the students about Lupin being a werewolf, and Lupin resigns as the parents of the students will not want a werewolf teaching their children.
When Voldemort returns in June 1995, the Order of the Phoenix is recruited and Lupin is in it again. With the death of Harry's godfather, Sirius, in June 1996, there is a good chance that in the 2 last books in the series Lupin will come closer to Harry.