When i envision cool its always 50's jazz artists that first come to mind, Thelonius Monk is the epitome of cool for me. Walking around on stage, humming, and that unique, sort of disjointed piano style, and the hip clothing, one suave dude! And I could go on and on with so many jazz and blues guys from 40's-70's.
John Lee Hooker, the voice alone makes him cool as hell!
Roy Orbison certainly cool, the shades man. Early Elvis.
Mick Fleetwood with the balls. Mick Jagger and James Brown had the moves. Just at top of mind Tony Joe White, Polk Salad Annie song, he was one of those swamp dogs, speaking of Swamp Dog, he's been going a long time. I could go on and on.