Ellsworth, a Black-eyed demon, is seen as the opposite of Bobby Singer; so Castiel claims. This demon works for Crowley and organizes the capture of the creatures used for finding that place.
The Winchesters find out from another demon that Ellsworth knew Crowley's location. Castiel goes ahead of them so he can clean the place out before they arrive. This way, they could never get to Crowley. Ellsworth is killed by Castiel, when Cas storms the place.
Ellsworth is a tribute to Jim Beaver's character on Deadwood.