I know a hepcat. Not fashionable and/or interested in swing music, Antoinette sells flowers outside Au Bon Pain at One Broadway, The One True Center of the Universe (at least as far as many New Havenites are concerned). She also knows the names, relationships, and business of a good number of people who pass by -- ask her whether So-and-so has passed by, and she'll tell you, also what they were wearing, which store they entered last, and so on. Very useful!
In African villages, the hepcat was an important person: sitting at the edge of the marketplace, he/she was a living bulletin board, messenger, and news/gossip/rumor source, just short of being one of the living geneologists you saw in Roots. On this side of the Atlantic, the word (originally "heppicat", or "one who has opened their eyes") got cut in two to become "cat" (as in random person) and "hip" (as in "hippie", or "someone who knows what's going ON!") Interesting, eh?