Old Harry. Old Scratch. To harry (Saxon) is to tear in pieces, whence our harrow. There is an ancient pamphlet entitled The Harrowing of Hell. I do not think it is a corruption of “Old Hairy,” although the Hebrew Seirim (hairy ones) is translated devils in Lev. xvii. 7, and no doubt alludes to the he-goat, an object of worship with the Egyptians. Moses says the children of Israel are no longer to sacrifice to devils (seirim), as they did in Egypt. There is a Scandinavian Hari = Baal or Bel.
Source: Dictionary of Phrase and Fable, E. Cobham Brewer, 1894