Furfur

In demonology, Furfur  is a powerful Great Earl of Hell, being the ruler of twenty-nine legions of demons.

He is a liar unless compelled to enter a magic triangle where he gives true answers to every question, speaking with a rough voice.

Furfur causes love between a man and a woman, creates storms, tempests, thunder, lightning, and blasts, and teaches on secret and divine things.

He is depicted as a hart or winged hart, and also as an angel. To some authors he changes from hart into angel when compelled to enter the magic triangle.