Crowley

Crowley is a powerful demon who was the King of the Crossroads and the King of Hell, following Lucifer's second re-imprisonment in his Cage. Although he initially served with Lilith as her right-hand man, he went rogue in Season 5 after her death and Lucifer's release, aiding the Winchester brothers in resealing the latter back into his cage. With the power vacuum in Hell unoccupied and with Ramiel's encouragement, he appointed himself the new King of Hell.

Crowley's role is often shifting from main antagonist to anti-hero. He was an anti-hero in Season 5, one of the three main antagonists in Season 6, an anti-hero in Season 7, the main antagonist of Season 8, and an anti-hero for the rest of his appearances. However, in all of his duration as an anti-hero, he is still openly an antagonist, usually pulling a life-threatening stunt on the Winchesters after assisting them. He is currently one of the longest lasting antagonists in the series, second only to Lucifer.