If you grew up in the 20th century, there’s a decent chance you wanted to be like Miles Davis, Billie Holiday, Humphrey Bogart, Albert Camus, Audrey Hepburn, James Dean or Jimi Hendrix. In their own ways, these people defined cool.
The cool person is stoical, emotionally controlled, never eager or needy, but instead mysterious, detached and self-possessed. The cool person is gracefully competent at something, but doesn’t need the world’s applause to know his worth. That’s because the cool person has found his or her own unique and authentic way of living with nonchalant intensity.
Source: How Cool Works in America Today