Earl o Hell noun
1 the Devil: They were engaged in this on a night as dark as the Earl o’ Hell’s waistcoat when suddenly a bloodcurdling scream rent the shadows ... 19-.
2 a Gypsy chief 19: This bold rebel was the leader of an inferior tribe [of Yetholm gipsies], and the immediate successor of another doughty chief, usually known by the appropriate title of the Earl of Hell.
19. etymology: Scots; attested by JS note:

The Dictionaries of the Scots Languague ( gives the following definition: A soubriquet applied prob. originally to the Devil