The story
sheep + biter (“one who bites”). Figurative term possibly influenced by the fable "De cane oves domini sui occidente, a quo suspensus est" in Hecatomythium by Laurentius Abstemius (later included with Aesop's Fables as "A Sheep-Biter Hang'd" — see quotations).
Etymology from Wiktionary, CC BY-SA 4.0.