detractor (n.)

"one who takes away from or injures the good name of another," late 14c., from Anglo-French detractour, Old French detractor "detractor, backbiter" and directly from Latin detractor, agent noun from detrahere "take down, pull down, disparage," from de "down" (see de-) + trahere "to pull" (see tract (n.1)).  The fem. form detractress is attested from 1716 (Addison).