House of Kath

"The Kath? I've never heard of them"
-Carrion De Rosa 
The House of Kath, also known as the Huxley Family, is an ancient and powerful demon clan founded by the The Great Kath, which ruled during an unknown era of Arkon. Famed for its genetic and black magic research, the clan grew to become immensely powerful, before being struck down by Axios the Divine. 
According to Kath doctrine, only a pureblood firstborn can become the demon lord of the house, and since all were killed off, the house has remained leaderless for millennia. The current head of the family is Raihan Zoraskaya, the first pureblood demon born since the clan's fall. 
During the Convergence, the primogenital line of House Kath was transported to Arkon's sister reality, Earth. After the event, the House of Kath adopted the last name Huxley and settled in London, the capital of Britain. From there, they have continued their duties in accordance to ancient Kath doctrine. 
The Kath does not only differ from other clans in this anti-leadership format, but also in the way of its succession. Due to the importance put upon the Kath Lord, the clan is far smaller than many may first expect. Instead of simply anyone who is descended or adopted into the house being a member of the clan, it instead follows the concept of absolute primogeniture, where only the eldest of the eldest can receive a clanmark. This results in a very small line of true Kath, with the only currently living members of the primogenital line consisting of Hela Kath-Huxley, Emily Huxley, and Leon Huxley/Raihan Zoraskaya. 
It has occurred in the past where members of the original primogenital line died off without heirs. When this occurs, the line jumps to the next of kin, making it vital that Kath clan members produce and successfully raise at least two to three children, in case one dies. However, there exists a certain glitch in the system, in which a previously deceased elder child is revived after the mark has moved, resulting in two lines of Kath. According to my research, this has occurred at least twice in history. The first was during the 11th era, when a Kath member was cured of an illness through the touch of a necromancer, resulting in a new line unknowingly splintering off. 
This second bastard line, known as the House of Zekundakath (Second Kath), still exists today, though has long since forgotten its past, and now consists only of a family of farmers that lives deep in the tribal regions of the Kondrak Mountains. The second instance of this was when Leon Huxley was stillborn, causing his mark to move to his twin brother Liam, but was later revived by the Great Kath, resulting in the birth of the first Demon Lord in a millennia, as well as the creation of the House of Tretakath (Third Kath).