The desolate island known as Monster Isle is near Japan. The network of tunnels that run beneath it lead to the Earth’s core. The monsters of Monster Isle appear to be mutate creatures created by alien intelligence.
The Isle was used as a base by the would-be world conqueror known as the Mole Man. The Mole Man established an underground empire and mastered the strange creatures, which included Giganto and the three headed Tricephalous. The Mole Man conducted attacks on the surface world until he was opposed by The Fantastic Four on their first adventure.