Who's This? The taxi driver on page 19 in Who's Who vol. XXI.
How you could have heard of him: The stuff of cheeky cameos ever since, Space Cabbie has been in everything from the Justice League Unlimited tie-in book to Lobo (his biggest role in modern comics, chasing down space bikers with the Main Man), from Starman to Books of Magic, from JLA: The Nail to Ambush Bug: Year None. Keith Giffen apparently intended to introduce Space Cabbie (or Cabby) in the New52's Threshold, but I don't think he got to it before the book was cancelled.
Example story: "The Luxury Limousine of Space" in Mystery in Space #45 (1958) by Otto Binder and Bernard Sachs, reprinted in DC Super-Stars #6 (1976)
Despite the silliness, I quite liked this unassuming little story, and I'd love to see some crazy Space Cabbie adventures at some point in the future (hopefully not concurrently with the year his stories take place). I wasn't kidding when I said I thought it would make a fun cartoon. Every week, a new fare brings a world of trouble on S.C. Shenanigans ensue. What do you think?
Who else? Thought about the Space Museum, but that's a "What" and might be a little similar to this entry. Instead I'm moving on to a horror character I know nothing about.