The Iwi are a tribe that inhabit Skull Island.
The Iwi are actually not native to Skull Island. Their ancestors actually migrated to Skull Island centuries ago. According to the Iwi, they lived in fear for centuries as the Skull Crawlers terrorized them. However, the ape super-species that ruled the island, who had a rivalry with Skull Crawlers, began to protect them over the centuries. They worshipped Kong and his species as their gods and saviors.
During a Monarch expedition in 1973, James Conrad, Reg Slivko, San Lin, and Mason Weaver encountered the Iwi, including Hank Marlow, a World War II pilot who was marooned on the island with Gunpei Ikari, (though the latter was killed by a Skull Crawler)