Where does the expression “a dog in the manger” come from and What does it mean?

Aesop, back about boo B.C., is said to have told his master about a dog which went to sleep in a manger full of hay.

According to the fable, the ox, for whom the manger had been filled, came up to it for his rations, whereupon the dog, roused from his slumbers, snapped at the ox and drove him away.

The ox, annoyed by this behavior, accused the dog of being churlish, because, he said, “You are unable to eat the hay yourself but will not leave it for those who can.”

Or, in the quaint words of John Gower, in Confessio Amantis, written about 1390, “Thogh it be noght the houndes kinde To ete chaf, yit wol he werne (prevent) An oxe which comth to the berne (barn), Therof to taken eny lode.”