lone gunmen

Noun

lone gunman (plural lone gunmen)

1. (idiomatic) An individual person who acts on his or her own initiative, without partners, especially one who has sole responsibility for doing something questionable, confidential, or iniquitous.
   • He continues, "So when someone blows the whistle, the hospital has to start looking for a scapegoat. The hospital looks for the lone gunman—the individual, acting alone, acting counter to his training, who, through a gross act of incompetence . . . ."2002, Jed Mercurio, Bodies, →ISBN, page 340

   Synonyms:

   maverick, rogue