Miles definitely created the cool vibe, but I suggest that Lalo Schifrin popularized it. Everyone knows the theme from Mission Impossible, but I think some of his best work was the soundtrack for Bullitt. The combination of the music, the car, the 60's San Francisco scene, the story and the King of Cool in the lead role really sealed the deal for me.
To this day, that soundtrack reminds me of how I got into music and continues to be a touchstone for how soundtracks should compliment and enhance a film. Today's score writers would do well to learn the lessons Schifrin bequeathed the industry.