Pandemoniac
Disco Infernal
That's the part that originated the movie style werewolf. The original legend had it's origin in the misinterpretations and lack of knowledge concerning physical and mental deceases, in a age filled with superstition.
The early werewolf tales cover a person sacrificing his humanity in exchange for power, mostly in a desire to avenge some vile act. Strangely, the same story appeared in Asia, among the Indians and in Europe before any of those nations ever came in contact with each-other.
In all cases, the werewolf is a being of great power, but remains mortal, and can be killed by 'ordinary mesuares'. Piercing it's heart or brain with any object or decapitation would do.
There are writings about reversing the 'curse' and returning the werewolf to it's human self, but just about as strange and complicated as the whole progress of becoming a werewolf.
As for me, just a legend that had to many tongues filling in details over the ages, while it was just a case of misinterpretation from the start