N'Kzak the Unnatural of the Mutated Nightblood race, in The Enchanted Lands.
While always a particularly loathsome and violent creature (even by nightblood standards), N'Kzak's power and murderous nature were amplified as the result of a conjurer's failed attempt to summon and control the beast. Since slaying this incautious fool, N'Kzak has become rage personified. Even other nightbloods avoid him, as his murderous rampages are chaotic and unpredictable.
Due to the effects of the conjuror's attempt to control N'Kzak, he is far stronger and more durable than a typical member of his race - and far less able to reason. His hide has the consistency of cross-linked armor, rendering it virtually immune to any form of slashing attack. He is also reputed to be more resistant to magic, divine and heat-based attacks than an average nightblood. Those unfortunate enough to do battle with him speak of his ability to electrically charge the air around him, causing tremendous magical damage to all unfortunate souls in the area.