Gaav was the mazoku lord directly responsible for the Water Dragon God (or Aqualord in the japanese version) Ragradia's death during the Kouma War 1,000 years before the current story,but was sealed into his human form by Ragradia attempting to duplicate the seal placed on the Dark Lord by Flare Dragon Ceifeed,the long deceased God of the Slayers world.
Gaav has sense lost interest in killing the remaining gods but is still as ruthless as he ever was.He started a war with the other mazoku lords after bargaining with the golden dragons to destroy all thier plans and took advantage of the God Sealing Barrier which required all the other lords to remain in one place and maintain each "corner",having made Lina Inverse a target for his minions to destroy upon learning the Hellmaster sent Xellos to accompany her.
Even in such a weakened state even the most powerful magics of the slayers world cannot harm him,and as a mazoku he can retreat to either the astral or material planes at will.
His true form is that of a crimson three headed dragon,and the spell Gaav Flare calls upon his power.
