The Culexus Temple is one of the most sinister and feared orders of the Officio Assassinorum and its Assassins have been described by Aeldari Warlocks as nothing short of the embodiments of pure evil. Even amongst the upper echelons of the Officio Assassinorum this temple is always viewed with extreme caution.

https://warhammer40k.fandom.com/wiki/Culexus_Temple
culexus assassin