The Iwi is a tribe that inhabits Skull Island.
As revealed in Skull Island: The Birth of Kong, the Iwi were originally not native to Skull Island, as their ancestors migrated to the island thousands of years ago. They arrived in time to witness Kong's parents towering above dead Skullcrawlers.
Originally, the Iwi had no formal language, and preferred to communicate with each other through gesturing and facial expressions; however, as revealed by Ato, during the events of Kong: Skull Island, Hank Marlow taught his father English, and his father taught it to him, in turn. This allowed the Iwi to evolve by developing their very own language.
They also worship Kong and his species as their gods and saviors, and fear the Skullcrawlers to the point of refusing to speak their true names.
Though not outright stated, or confirmed, it would appear there is something of a hierarchy in the Iwi's society, as Ato has blue tribal tattoos adorning him, and many others (presumably the various leaders) also featured blue tribal tattoos, whereas all the others had yellow tattoos.
Tactics and weapons
Due to their "primitive" lifestyle, the Iwi primarily use "ancient" weapons such as spears and bows. They also prefer to ambush their enemies, as many painted their skin to blend in with the stone architecture surrounding their village.