Who's This? Who's Who vol.VII, bottom of page 15, this ugly puss:
How you could have heard of him: Apparently, Earthworm survived the end of the multiverse because he was next seen getting a power boost from Neron during Underworld Unleashed (UU #1), to he could face Guy Gardner (in GG:Warrior #36). Given the 90s art on that, they managed to make him look even grosser.
Example story: Wonder Woman vol.1 #309-313 (1983-84)
His complete absence until Underworld Unleashed makes his presence there slightly dubious since the villains who sign with Neron presumably have a loser's CV they're trying to get away from. So in the revised continuity, did Earthworm still fight (the Bertinelli) Huntress? Was he actually defeated by her or some other hero? In any case, Neron makes him a demon with stretchy arms and a "digging" ability, but also the same rat-controlling powers. Making him more like his namesake I think made him less compelling, but I'm probably responding to the 90sness of it.
Who else? I think I'm done with volume VII of Who's Who for now. I might have done the Jonah Hex villain El Papagayo, but I think we know what Hex stories are like. I have very little interest in Flash villain the Eradicator, but I might do him and the Fadeaway Man on the next pass.