E. Cobham Brewer 18101897. Dictionary of Phrase and Fable. 1898.
A jackal; a foil to another mans wit, a humble friend who plays into your hand to show you to best advantage. The jackal feeds on the lions leavings, and is supposed to serve the lion in much the same way as a dog serves a sportsman. The dog lifts up its foot to indicate that game is at hand, and the jackals yell to advertise the lion that they have roused up his prey. (See JACKAL.)