Monster Island was originally introduced in the 1969 film All Monsters Attack, in the dreams of a young boy named Ichiro. He dreamt of befriending Minilla (son of Godzilla) and watching him and Godzilla battle other monsters.
Since its first introduction in 1969, the concept of Monster Island has been used in multiple projects across all forms of multimedia. The second most popular version of the island is from Marvel.
Monster Island (or as it was originally called, Monster Isle) is located in the Sea of Japan at longitude 136, latitude 40 degrees north. Monster Island is perhaps the most famous dwelling place for monsters in the world. The small and ruthless Mole Man used the island as his base of operations.
It got its name from the strange monsters that inhabit this would-be paradise. The island has caverns that run down into the core of the planet, these caverns connect the island to the continents of the planet. The caverns also provide refuge for the subterranean monsters.
The Mole Man established himself in Subterranea, which would become his underground empire, where he learned to master the strange creatures.
Monster Island was thought to be destroyed by the Mole Man in his attempt to destroy the surface world, by using an underground atomic explosion. The island appeared to show no signs of harm from the detonation. Much later, the protectors of the Infinity Gems, Adam Warlock and the Infinity Watch, would use the island as their base of operations.
Although the Mole Man claimed the island for his underground empire, the United Nations never recognized it as a nation of its own. They have made several attempts to invade the island.
Dinosaur Island was often called Mystery Island or Monster Island during its initial appearances in Star Spangled War Stories.
In the Warren Ellis series Planetary, there is Island Zero, home to many kaiju. However, it appears that King Ghidorah, Godzilla, and Mothra are all dead. A flying green kaiju resembling Rodan has survived.