He is our benefactor. Without his power and knowledge we would not be where we are today. A few souls is a small price to pay!
Demon Lord Onath is from an hell dimension and has been supporting the members of the Weaver family for several centuries. This pact was created with many blood sacrifices to supply the Lord with human souls. What exactly he does with the souls is unknown, but his need for more souls never ends.
He has supported the family very reliable, but is known for his cruelty. He prefers souls of people who have suffered major trauma during their lives. His interest in the human realm is also in its culture, people and cruel history. He is fascinated by tales of wars, genocides and other events of cruelty and destruction.
The demon lord holds power over a small domain in his world. The demonic familiars
of the Weaver family are all summoned from this domain to do their bidding. It is through these familiars that he supports the family.
He can strengthen and empower any magic used by a Weaver family member to ensure that they are more powerful than their opponents. He also shares some insight into ancient magics and improves their health and constitution slightly. Though this slight improvement rarely helps them survive being murdered by each other.