When you think about it, he was Marvel's first villain and, right from the start, Stan Lee & Jack Kirby imagined a great character :
- He controls giant monsters ! He and his monsters fill the gap between the Monster Age & the Marvel Age, just like the Thing & Hulk.
- He is the first sympathetic Marvel villain (not counting Namor). He is a misunderstood outcast with a tragic past. Like the Phantom of the Opera, he hides in darkness because of his ugliness. He has been portrayed as a complex character since his first appearance, way before Dr. Doom & Magneto. Sometimes, he initiates attacks on the surface world but, other times, he only tries to protect his kingdom from harm.
- He is the first "animal-totem" Marvel character, before Spider-Man, Chameleon, Vulture, Doctor Octopus, the Owl, the Eel, the Beetle, Captain Barracuda, the Fox, Black Panther ... and so many others.
- He is the first "M" villain, before Miracle Man, Magneto, Molecule Man, Mastermind, Maximus the Mad, Mentallo ... and so many others. Of course, like many Marvel characters, he has an alliterative name. He is also the first Marvel villain to wear green & purple costumes.
- Before Daredevil (and Spider-Man), he is the first Marvel character with a radar sense and, before Alicia & Matt Murdock, he is the first (nearly) blind Marvel character. Actually, he isn't really blind but his eyes can't stand light. Just like Cyclops, he has to keep his glasses on (in his case, to protect his eyes from light). Just like Daredevil & Kingpin, he carries a walking stick that conceals hidden tools & weapons.
- He is the first Marvel villain who is at the same time a scientific genius, a good fighter and a political leader. He is also the first Marvel character (not counting Namor) who is the ruler of an exotic kingdom (before Dr. Doom, Black Bolt, Black Panther ...).
- He might be the first of the FF's Paracelsian elemental characters : Mole Man might represent the Earth Gnome, Dragon Man might represent the Fire Salamander, Air-Walker might represent the Air Sylph and Lady Dorma might represent the Water Undine.
- Although most people are not aware of this, he might be one of the most powerful villains on Marvel Earth. He is a scientific genius. He has an army of minions and giant monsters. he might be the richest man on Earth thanks to his direct access to huge mineral resources (for example, the Valley of Diamonds). He can trigger earthquakes around the world. He might still know where the Fountain of Youth is.