instigator (n.)

early 15c., instigaccioun, "urging, incitement; impelling force," from Old French instigacion "instigation," and directly from Latin instigationem (nominative instigatio), noun of action from past-participle stem of instigare "urge on, incite," from in- "in" (from PIE root *en "in") + *stigare, a root meaning "to prick," from PIE root *steig- "to prick, stick, pierce" (see stick (v.)).