Lone Wolf

Just learned a new word: Lone Wolf.

From Wikipedia:
As a person, a lone wolf is an individual who prefers solitude, is introverted, or who works alone.
In literature, lone wolves are aloof and emotionally unable or unwilling to directly interact with other characters in the story. A stereotypical lone wolf will be dark or serious in personality; they are often taciturn, and will distinguish themselves through their reserved nature.

From the media:
Teroris yang bertindak sendiri dan tak berafiliasi dengan organisasi internasional.