perturber
/pəˈtəːbə/noun
1A person who or thing which perturbs; a disturber; a troublemaker, a transgressor.
2 Physics. A particle which interacts with a radiating atom or ion, affecting the wavelength of the emitted radiation.
Origin
Late Middle English. From perturb + -er. Compare Anglo-Norman partourbour and Old French pertourbeor.