The Hunt for Remus Lupin
Most would think that childhood would be rough enough without a curse. Remus was bitten by a werewolf at a young age. It's not yet clear how this happened, but once the deed was done, there as no undoing it. There is no cure for the bite of a werewolf, and under every full moon, his body would rip itself apart and slam back into the shape of a wolf.
Naturally, this condition would make it difficult to attend Hogwarts, sharing a room with other children every night. Luckily, Headmaster Dumbledore made special arrangements for him, having a tunnel built to get Remus out of the castle on the full moon nights. The Whomping Willow was planted to guard the tunnel against the curious.
From there, Remus was able to get to an empty house and lock himself in. His screams and howls and his attacks on the inside of the room earned the house a reputation as being haunted, which only helped protect his secret. He couldn't hide it from everyone, though. His three best friends soon found out and studied their own shapeshifting spells so he wouldn't have to be alone anymore.
His worst enemy also found out about it though and, though sworn to secrecy about it, Severus Snape has had nothing positive to say about Remus to this very day. He did help him by making the potion that helps keep his werewolf bloodlust down, but there appears to be some serious animosity. It's hard to blame Snape for this when you consider that he was nearly killed by Remus, thanks to a dark prank by Sirius Black...Remus had no way of stopping himself in his werewolf state and this has been a very sore spot between them for many years.
After Hogwarts and the death of the Potters, Remus wandered to many places, learning the sort of information that would make him the students' favorite for Defense Against the Dark Arts teacher, but never being accepted. His curse kept anyone from trusting him, no matter where he went.
Dumbledore gave him the chance, once again, to find a place at Hogwarts, where he did become the D.A.D.A. teacher. It also brought him into contact with old rival Snape, the son of his best friend, Harry Potter, and, would throw him in with his oldest friends, Sirius on the run from the law, Peter hiding from his own betrayal, and James,if only in spirit as the Patronus Prongs.
In the end, Remus was set adrift again. Snape let slip the truth about his lycanthropy, and knowing that no one would want him near their children, Remus packed up. He's lived the life of a lone wolf a long time, and maybe he's only waiting to join up with Sirius again. They are the last two members of their original circle of friends, with James betrayed and Peter the traitor. Like Sirius and Peter, it's anybody's guess as to when we'll see him again.