Atticus

 Atticus was born from the darkness within Dean Winchester by Crowley's hand. Crowley created Atticus to serve him with the idea of making him a powerful demon who'd only obey him. Soon after Atticus was created, he developed a mind of his own and quickly overthrew Crowley by appealing to the demons in a way he couldn't. Atticus rallied an army of demons on his own, and temporarily reigned until he was thrown into Purgatory by Nate and Rellus, with the help of Crowley.

Months later he appeared in one of Nate's visions alongside a woman with dark hair and skin, which was quickly dismissed due to everyone's disbelief. Surely enough, the rise of Atticus was imminent and he and Ramiel joined forces when the prophecy was fulfilled.