Who's This? The sword & sorcery guy on the last page of Who's Who vol.XVI.
How you could have heard of him: After Who's Who, Nightmaster made a few cameo appearances, trading on his obscurity, and more weighty appearances in Primal Force and Swamp Thing in the mid-90s. Of course, modern readers know him as a member of Shadowpact, the Oblivion Bar they worked out of actually named after the old store, Oblivion Inc., that served as a doorway to the fantastical world of Myrra.
Example story: Showcase #83 (1969)
Who else? The New Olympians aren't big names, but my next Outsiders posts will talk about them at length. Night and Fog were minor All-Star Squadron villains that were fairly recent when Who's Who came out. No, I think Nightmaster rounded out vol.16 well enough. It's on to the next issue...