noun. One that stirs up trouble or strife.

noun. One who causes trouble, especially one who does so deliberately.

noun. A complainer.

noun. someone who deliberately stirs up trouble

"The conductor/pianist/Olympic-class troublemaker is also promoting his new memoir, Music Quickens Time (at least that's the American title, anyway)."

persona non grata  unwelcome person  

Heller  agitator  badgerer  blusterer  cut-up  

aggressor  blackmailer  coxcombs  dissident  egoist  

agent provocateur  agitator  agitprop  catalyst  complainer