In the
fantasy novels of
Rick Cook, a terrible
slaying
demon that was capable of killing almost any
creature possessing a true name. It did not matter whether the true name of the victim was
known to either Bale-Zur or its
controller; it was sufficient for it to have been
spoken at any time within the World. Bale-Zur's physical appearance was of an
enormous black shape with a
horned head, glowing red eyes, and huge, cruel
talons.
Bale-Zur was originally used as a guardian for the tomb of the great evil wizard Amon-Set. When Shiara the Silver and Cormac the Golden set out to enter the tomb and retrieve its magic items for safekeeping, they first had to neutralize the demon. Shiara was forced by circumstances to destroy the tomb, and only the demon remained...to be found by the Dark League wizard Toth-Ra, later called Toth-Set-Ra, who bargained with Bale-Zur to gain the ascendancy of power within the Dark League.
Toth-Set-Ra later made the mistake of trying to turn Bale-Zur against Wiz Zumwalt, whose true name (William Irving Zumwalt) had never been spoken within the World. Bale-Zur, their bargain broken, killed Toth-Set-Ra and escaped, roaming the City of Night. When Wiz was later kidnapped by remnants of the Dark League, he led them into a confrontation with Bale-Zur that resulted in their deaths.
Bale-Zur continued to roam the City of Night looking for victims, ranging farther and farther across the Southern Continent. It was feared that it might one day use its power to travel across the Freshened Sea, and so an expedition was mounted, headed by Wiz (who first had to destroy a hunting demon waiting for him), which located the heart of the demon and neutralized it once and for all.
Sources: Rick Cook, Wizard's Bane, The Wizardry Compiled, The Wizardry Cursed