Zath's origins are unknown. It has some connections to the Spider-god Omm, but whether Zath is Omm's offspring or descendent, or whether it is the reincarnation of Omm itself, is currently unknown.
Worshiped during the Hyborian Era in Yezud. Priest would raise Cattles which were used to feed Zath. A statue was also made in it's honor.
Zath eventually made thousands of progeny. The Priests of Zath sought to raise the Children of Zath to use as an immense army to conquer all of Zamora, taken rule from King Mitradites.
Conan returned to Yezud, hoping to rescue the kidnapped Jamilah, in the hopes of having her husband remove the bounty on his head. While freeing Jamilah, he learned of Feridun's plans for the Children of Zath, and subsequently encountered and incapacitated one of them. Conan fell in love with one of the Dancers, Rudibeh, who helped him hide out in the temple. In the basement, however, Conan encountered the monstrous Zath itself, and even his great strength seemed to be futile. Zath, however, turned upon hearing the voice of Rudibeh, who had come searching for Conan, and Zath instead found and slew her.
As Conan attempted to escape, he wandered into the lair of the Children of Zath. Conan managed to escape out of a trap door, and set the basement on fire. Zath burst through the temple walls, to escape the fire, although Feridun attempted to prevent Zath's exodus. Initially, Feridun's magical incantations were quite effective, until the smoke in the air choked him up--at which point Zath lunged forward and slew him. Conan threw several torches onto Zath's back, and, unable to put them out, its death-throws toppled the temple, slaying and/or trapping many of its children within. Conan convinced many of the soldiers of Yezud to attack the remaining, weakened Children of Zath, and they were apparently all slain as well.