As I was working on my Atrapos and though of an origin story. A house that got decimated fighting on a long lost forgeworld. They arrived at it and woke up it's automated defenses. The campaign to claim it went horribly as the defenses were arcane and extremely effective and included drone Magaera and Stryx knights. The Seneschal survives and seeks shelter in an underground manufactorum where a partially assembled Atrapos waited. Getting it running he discovers the planets defenses are slaved through the Atrapos' animus and through bonding with it claims the world for himself. With an army of drone knights he flings himself into the stars to claim as much as he can.