To be excessively cruel or tyrannical. Herod was the King of Judea who according to the New Testament ordered the deaths of all male babies in an attempt to kill Jesus. That dictator could out-Herod Herod with his fits of violence.
out-Herod Herodbehave with extreme cruelty or tyranny.
Herod, the ruler of Judaea at the time of Jesus's birth and the man responsible for ordering the massacre of boy babies in his realm, was portrayed in medieval miracle plays as a blustering tyrant. The phrase is from Shakespeare's Hamlet : ‘I would have such a fellow whipp'd for o'erdoing Termagant; it out-herods Herod’.