instigator
1. [ noun ] someone who deliberately foments trouble
Synonyms: inciter instigant firebrand provoker
Examples:

"she was the instigator of their quarrel"

Related terms: troublemaker ringleader harass incite
2. [ noun ] a person who initiates a course of action
Synonyms: initiator
Related terms: leader aggressor initiate
Similar spelling:   instillator
  instigate
  instigant
  instigative
  instigation
  instilling
  in_store
  instructor
  institution
  instantiate
  instinct
  ingathering
  institutional
  institute
  instantiation
  insatiate
  insatiably
  insatiable
  inactivate