1950s? James Dean?
I vaguely remember speculating in some piece that cool lies in being a master of technological modernity without being defined by it. Usually goes with a powered artifact like a motorcycle. Spirit machine. Mastering a horse made you heroic but not cool.
Does cool in jazz have the same connotations as cool in general culture?
I’ve always thought of it as more of a detached, cerebral version of the more involved depressive mood of the blues. But general cultural cool is more shallow.