The Lava Men were first revealed to the Marvel Universe readers in the pages of Journey Into Mystery #97 when he battles a lone Lava Man. I love the way that Jack Kirby and Don Heck rendered the Lava Man in this story, he's very distinctive and menacing. (I notice on the cover that Kirby has borrowed the old Alex Schomburg trick of having the hero and the villain presented much larger than the fleeing folks below.) This was of course at a time when Marvel was only just beginning to get a sense of each book participating in a larger universe, so the Lava Man was created without regard to any other subterranean race.
The Lave Men show up as a race when they battle the Avengers in the fifth issue of that venerable run. Like the Moloids and the Tyrannoids the Lava Men were a variation of life created by the Deviants during their never ending experimentation with the genetic code imparted to them by the Celestials. Spectacular stuff!
More to come when we meet more disparate Deviants on Monday when the Gortokians show up.