Headless Horseman

The backstory told by Brom Bones was accurate. Filling in the gaps, it was the Friends that allowed his body to continue living after his head was blasted off, giving him a new mouth for which to digest victims with, terrorizing Sleepy Hollow in search of a head. He killed several before Ichabod Crane, but he never found one that suited him. He continues to terrorize the town, even if he's found his head, because his debt has not been repaid. Despite this, he was at one point responsible for saving the infant daughter of a wealthy family, meaning he at one point wasn't a total villain.

Depending on your interpretation of the story, the one who has the deal with the Friends could be Brom Bones. He summoned (or was temporarily transformed into) the Horseman to destroy Ichabod. In the end, however, he couldn't go through with it, but still chased him out of town. Either way, Sleepy Hollow had the Friends' fingerprints all over it.
He also has a protégé named Headless Lester, who stalks a summer camp.