Skull Island, also known as Island #11002039543, is a tropical island, surrounded by dangerous storm systems, located in the Pacific Ocean. The island is home to a plethora of immense creatures, the largest of which is Kong: the last of an ancient primate superspecies worshiped as a deity by the island's human inhabitants.
Skull Island was a highly dangerous location and was home to an entire ecosystem of M.U.T.O.s: the most notable being Kong and the Skullcrawlers. Monarch hypothesizes that the island's super-contained biome allowed evolution to take on a different path, producing gigantism unseen in other forms of megafauna. Other known creatures on the island included the spore mantis, tree dwellers, and Mother Longlegs. Some of these creatures were known to be entirely new lifeforms: a mixture between flora and fauna termed "Flora-fauna" by Monarch operatives.
The island was also home to a primitive tribe of humans called the Iwi.
Most notably, the island's bedrock was entirely hollow. These hollow spaces beneath the island were the habitat of the skullcrawlers.
In prehistoric times, Skull Island was inhabited by a species of enormous primates who were constantly at odds with the carnivorous skullcrawlers. By the time of Kong's birth, there were only two of these primates left. After his parents' deaths, Kong became the last known member of his species.
After the advent of humanity, Skull Island became a mythological location, deemed to be beyond the laws of the natural world, throughout several cultures in Oceania. At some point, the island was settled by a tribe of humans who came to worship Kong as a god.
Sometime after the events of the 1973 expedition, Monarch established an outpost on Skull Island.