Definition of "instigator"

[T]he Pope doth not keepe his quarter, but will needs breake forth of the rayles and limits of that diſtinction, taking vpon him to be authorized alſo temporally, and that, for the ſuppreſſion and ſubverſion of the Civill Soveraignity, […] whence muſt neceſſarily ariſe either privie complottings, or open attempts, in favour of their opinions, and in furtherance of their deſires, which how farre it will extend, and into how deepe degrees it vſeth to grow, many ſorowfull and fearefull examples hath in this Realme demonſtratively declared vnto vs, to every whereof Papacy hath beene the ſtirrer and inſtigator.

1606, Edvvard Forset [i.e., Edward Forsett], “An Examination of a Position Published by P. R. in the Preface of His Treatise, Tending to Mitigation, Concerning the Lawfullnesse of the Popes Power ouer Princes: With a Defence of the Oath of Allegiance”, in A Comparative Discovrse of the Bodies Natvral and Politique. Wherein out of the Principles of Nature, is Set Forth the True Forme of a Commonweale, with the Dutie of Subiects, and the Right of the Soueraigne: Together with Many Good Points of Politicall Learning, Mentioned in a Briefe after the Preface, London: Printed for Iohn Bill, page 92

[H]e [Jesus Christ] whom they deſpiſed as the Carpenters Sonne and bad come downe from the Croſſe, if he could, is exalted to the right hand of God, having all judgement committed to him, having before hand in his death, judged, ſentenced, & overcom Sathan the Prince of this World, the chief inſtigatour of his crucifiers, who had the power of death.

1648, John Owen, “An Answer, to the Twentieth Chapter of the Booke Intituled, The Universality of Gods Free Grace, &c. being a Collection of All the Arguments Used by the Author, throughout the whole Booke to Proove the Universality of Redemption”, in Salus Electorum, Sanguis Jesu; or the Death of Death in the Death of Christ. A Treatise of the Redemption and Reconciliation that is in the Blood of Christ with the Merit thereof, and the Satisfaction Wrought thereby. [...], London: Printed by W. W. for Philemon Stephens; and are to be sold at his shop at the Golden Lyon in St Pauls Church-yard, book IV, page 279

The author (obviously a naturalist of no mean order) received an official rap over the knuckles for trespassing, and for encouraging others to do so. Evidently the instigator of this reprimand had not visited the railway in blackberry time!

1950 March, Eric S. Tonks, “The Whitacre—Hampton-in-Arden Line, L.M.R.”, in Railway Magazine, page 187

In studies designed to arouse aggression, the instigator often not only threatens the subject, but also expresses an extremely high self-evaluation. Subjects are insulted about their intelligence, sexual attractiveness, and character, and, at the same time, the instigator implies or explicitly describes his own superiority in these respects.

1964, Albert Pepitone, “The Reaction to Boastfulness”, in Attraction and Hostility: An Experimental Analysis of Interpersonal and Self Evaluation (The Atherton Press Behavioral Science Series), New York, N.Y.: Atherton Press, OCLC 490312942; reprinted New Brunswick, N.J.: Aldine Transaction, Transaction Publishers, 2009, page 77

The instigator has the power to start the conflict. The person instigating the conflict always seeks power in some form. That is why they are starting the fight. […] An example of this is a child who tells two different kids that they are saying things about each other. This then starts a fight between the two kids, and the instigator gets to watch the fireworks. The instigator likes to feel the power of seeing the other two kids fight. In some cases, the instigator may want to redirect attention away from him- or herself and onto someone else.

2004, Erik A. Fisher, Steven W. Sharp, “The Players”, in The Art of Managing Everyday Conflict: Understanding Emotions and Power Struggles, Westport, Conn.: Praeger Publishing, Greenwood Publishing Group, page 55

Although each [river] restoration is unique, the genesis of most projects appears to center on a singular sort of individual that I have come to call "the instigator." Instigators are typically average Americans, quite often from a background that we would not consider a position of power. They are "housewives," students, small business people, retired persons, or a local politician or government administrator.

2012, Daniel McCool, “Crumbling Edifice”, in River Republic: The Fall and Rise of America's Rivers, New York, N.Y., Chichester, West Sussex: Columbia University Press, page 12