There's a theory that Draco Malfoy from the Harry Potter series is actually a werewolf. Here's some proof (this will go by the books, not the movies).
In the first five books, Draco is nothing more than a rival to Harry, and is an average bully. But in the sixth book, Draco becomes much more stressed out. Harry sees Draco in Borgin & Burkes reveal something on his arm. Harry assumes that it is a Dark Mark, but this is never seen (it was seen in the movie, not in the book). Harry sometimes tends to jump to conclusions, but Hermione doesn't think he's a Death Eater and Hermione is usually right.
Fenrir Greyback, a werewolf, is introduced, sent to bite the children of those who had failed Voldemort, which is why Remus Lupin is a werewolf. And Draco's father, Lucius, isn't exactly the best Death Eater. In the second book, he failed to bring Voldemort to power and ended up causing one eighth of his soul to be destroyed and in the fifth book, he failed to bring Voldemort the prophecy. So it makes perfect sense for Voldemort to want Lucius' son to be bitten. It also adds to the reason Lucius and his wife, Narcissa turn on Voldemort and lie to him about Harry's death.
Also, after the Death Eaters discover that Remus and Tonks are having a son, Voldemort says to Draco, "Maybe you can babysit the cubs", but what is this supposed to mean as an insult? Perhaps Voldemort is suggesting to Draco that it doesn't matter if you get bit because you've already been bitten. There's also a hint that Draco does not have a Dark Mark. The Death Eaters set up a barrier in the Astronomy Tower that you can only pass through if you have a Dark Mark. It goes up after Draco goes through and comes down right before Draco comes down.
And if Draco doesn't have a Dark Mark, what else could he have shown Borgin that could have scared him so much?
This theory is plausible, but has been said by J.K. Rowling that it is not true.