Adonael: Latter generation Arch Angel. Hybrid of dakness mixed with Arch Angel Michael's essence, among some others.

Adonael: Was banished to the void for betraying the Tall, Blond, Elder ones. In the void he met Abbadon

Abbadon: Angel of Death and Destruction. Fell after making a pact with a spider Goddess and killing his family (As a sacrifice)

Adonael and Abbadon become one while inside the void, and their power combined allowed them to escape to a new world. 

To become: The Black Knight.