African-Americans invented cool as a stylistic defiance against racism during
World War II. This is simply well-documented social, historical, and
linguistic fact. To be cool in the 1940s referred to the ability to be relaxed in one's own style in any
environment, an act of courage and mental strength for any Black person during the Jim Crow era. Whether meaning high praise ("Cool!"), vetting someone to others ("she's cool"), or referring to a relaxed state of mind ("I'm cool, man") -- our modern usages all began in jazz culture.