Origins of the expression
The expression dates back to Roman times.
The Senate declared emperor Nero a hostis publicus in AD 68. Its direct translation is "public enemy". Whereas "public" is currently used in English in order to describe something related to collectivity at large, with an implication towards government or the State, the Latin word "publicus" could, in addition to that meaning, also refer directly to people, making it the equivalent of the genitive of populus ("people"), populi ("popular" or "of the people"). Thus, "public enemy" and "enemy of the people" are, etymollogycally, near-synonyms.
The words "ennemi du peuple" were extensively used during the French revolution. On 25 December 1793 Robespierre stated: "The revolutionary government owes to the good citizen all the protection of the nation; it owes nothing to the Enemies of the People but death". The Law of 22 Prairial in 1794 extended the remit of the Revolutionary Tribunal to punish "enemies of the people", with some political crimes punishable by death, including "spreading false news to divide or trouble the people".