The characters were from the invisible city Mourningstar.
Mourningstar is a city built on the back of a giant sleeping turtle floating in the astral sea.
Although most of the PCs were too young to remember it, they were sold to the arcane guilds of the city as children by slavers.
sooooo...
An asteroid made from the shadows between the stars struck Monde three centuries ago turning most of this small forested planet into uninhabitable desert. The majority of the inhabitants that were not killed outright were warped into horrific creatures. The few survivors banded together into semi-nomadic tribes, many of which turned to cannibalism and began worshiping dark powers.
Killominatu was born into one of the few nomadic hunter tribes not corrupted by the asteroid or desperate enough to begin eating each other. When his people were destroyed by a band of foulspawn led by a deathpriest of Orcus his two older brothers fled with him deep into the desert wasteland. Dehydrated and starving the brothers could not escape the slavers that found them a few weeks later. Although the conditions in Mourningstar are sometimes harsh and brutal for non arcane slaves, Killominatu still laughs at the threats from his masters, compared to the horrors of his home world he considers this paradise.