A Werewolf
Morgoth originally produced Werewolves by magically altering his minions' forms so that they became huge, enchanted Wolves. He created others by placing undead spirits in the bodies of great Wargs.
The greater Werewolves are Maia-Spirits of great power while the lesser Werewolves - or true Wargs - are but mighty undead beasts.
These creatures can alter their form so that they can stand upright and use their clawlike hands, but they cannot transform themselves into Men. While Werewolves possess the intelligence of the Secondborn — and though they can speak, use tools, and cast spells — they remain Wolf-like in their nature. Only a few maiarin Werewolves still possess the ability to change their form into a more human-like appearance.
MERP
In MERP, the Term Werewolf is also sometimes applied to mannish-werewolves, shapeshifters or beastmen, created by Dark Magical experiments.