At the height of the illithid empire, the mind flayers captured kuo-toa by the thousands and forced them into bondage. The kuo-toa were simple creatures, never meant to endure the oppressive mental force the illithids unleashed against them. By the time the mind flayers abandoned them, the prolonged psychic subjugation endured by the kuo-toa had driven them mad.
Their minds shattered beyond repair, the kuo-toa adopted a religious fervor, inventing gods to protect them against threats. Most notable of these threats are the drow, which have slain the kuo-toa on sight since the days when the two races first met.