Ready Reference: Vigilante

According to Merriam-Webster, the word vigilante can be defined as:
"a member of a volunteer committee organized to suppress and punish crime summarily (as when the processes of law are viewed as inadequate); broadly : a self-appointed doer of justice."

Etymology:
Spanish, watchman, guard, from vigilante vigilant, from Latin vigilant-, vigilans

First Known Use: 1856

Wikipedia gives a brief history:
"Several groups and individuals have been labeled as vigilantes by historians and media. Vigilantes have been central to several creative fictional works and in some cases have been depicted as heroes and retaliatory forces against wrongdoers.

Vigilantism and the vigilante ethos existed long before the word vigilante was introduced into the English language. There are conceptual and psychological parallels between the Dark Age and medieval aristocratic custom of private war or vendetta and the modern vigilante philosophy.

Recourse to personal vengeance and duelling was considered a class privilege of the sword-bearing aristocracy before the formation of the modern centralized liberal-bureaucratic nation-state (see Marc Bloch, trans. L. A. Manyon, Feudal Society, Vol. I, 1965, p. 127). In addition, sociologists have posited a complex legal and ethical interrelationship between vigilante acts and rebellion and tyrannicide.In the Western literary and cultural tradition, characteristics of vigilantism have often been noted in folkloric heroes and legendary outlaws (e.g., Robin Hood). Vigilantism in literature, folklore and legend is deeply connected to the fundamental issues of morality, the nature of justice, the limits of bureaucratic authority and the ethical function of legitimate governance.During medieval times, punishment of felons was sometimes exercised by such secret societies as the courts of the Vehm (cf. the medieval Sicilian Vendicatori and the Beati Paoli), a type of early vigilante organization, which became extremely powerful in Westphalian Germany during the 15th century."

Synonyms:
avenger, castigator, chastiser, punisher, scourge, nemesis