Who's This? On page 23 of Who's Who vol. XXI, he's the undead-looking guy.
How you could have heard of him: Young All-Stars #18-19 (1988) did feature a Frankenstein's Monster who called himself Victor Frankenstein II who was at least inspired by the Spawn, but these days, the creature simply known as Frankenstein (from Grant Morrison's 7 Soldiers, and from the first wave of New52 books) is how we remember Vic I's creation.
Example story: Phantom Stranger #23-25 (1973) by Marv Wolfman and Mike Kaluta
So did any of this happen in Frankenstein's current continuity? I guess it did. Only the Flashpoint version was awakened during WWII, so the 7 Soldiers and New52 Franks could have been unfrozen from the 70s on.
Who else? I'm ready to move on to the next issue of Who's Who, but may one day return to such characters as Spellbinder, Spanner (and his Galaxy) and even Stalker, which I've left alone for now. Place your bets for who I'm going to cover in volume 22: Starfire I to Syonide.