Skizzix

The Skizziks were a human family from Sigil that feared annihilation from their rivals. They made a pact with Asmodeus to become tieflings and they were awarded devil servants who act as their bodyguards and assistants.

At one time, Omin Dran had an infernal contract that allowed him to call forth the family's most powerful member: Strix.

The "Skizziks Khasrym" sent a mercykiller and two chronikers to Camp Vengeance to abduct Strix. The group fought back, and ended up in Sigil for a short time. They destroyed the mercykiller and saw a few tieflings nearby who may have been linked to the Skizziks. The tieflings were arguing about whether or not to intervene: Strix asked the oracle at Orolunga about the Skizzixes. The naga said that she knew someone who looked like Strix, and that "All will be made clear when you meet yourself."
 * A female, short and old.
 * A male, tall and proud.

When Strix met "Ubtao", he told her that the Skizziks are a human clan who made a pact with devils that transformed them into tieflings.

She furthered learned about the Lorcatha clan, who are linked to angels.

A deal known as the Ashton Concordance kept the two families in a cease fire/non-interference pact. One of the terms of this pact is that members of the two clans can't have anything to do with each other or the multiverse might be destroyed.

Also, the Lorcatha had to give up their souls... all except one, who apparently is Diath.