perturber

noun2

1. •
   One who or that which perturbs.

   • The queen forgot the dignity of her station and the softness of her sex, and, in language more fit for the markets than the court, called him rogue, and traitor, and perturber of the public peace; […] — 1836
2. •
   A source of perturbation.

   • This moon is a significant perturber.