Who's This? It's NOT the Spirit, there on page 16 of Who's Who vol.XV, but I don't blame you for thinking it was.
How you could have heard of him: Roy Thomas gave him a rather serious origin in Secret Origins #28 with art by Gil Kane, and did use him as a member of the Freedom Fighters in equally serious issues of All-Star Squadron (most prominently, #31). John Arcudi's JLA: Destiny (an Elseworlds), used a Midnight character with the secret identity William Cole, obviously an homage to Jack.
Example story: Smash Comics #84 (1949) by Jack Cole
Jester stories also in Smash Comics, and not surprisingly, both strips were handled by Paul Gustavson at a crucial time. As this is a Jack Cole story, the zanies are well served by lots of slapstick going on in the background, breathing life into standard exposition panels. It's very Mad Comics.
It's kind of sad there's no room for a character like Midnight anymore. For one thing, he's visually too close to the Spirit. For another, the company that owns him, isn't into doing comedy these days. Even in the 80s, Roy Thomas, the guy who should have been Midnight's protector (just as he protected other Golden Age characters) turned him into a serious and thus unremarkable crime fighter. There's nothing interesting about that take, save the name.
Who else? Next week, I think I may be doing a three-for-one Who's This feature. Take a guess (no cheating if you've read my comments about the latest Who's Who Podcast on Firestorm Fan).