Well, Tamatoa hasn't always been this glam, he was a drab little crab once. Now he can be happy as a clampearl, "Because I'm beautiful, baby!"

Tamatoa is a Gargantuan Coconut Crab, also commonly known as a Robber Crab, Bandit Crab, Pirate Crab, or Palm Thief. Coconut Crabs are a type of fully terrestrial Hermit Crabs that use Coconuts as shells when they are younger and eventually outgrow the need for having a shell becoming the dominant predator on their Islands, they have been known to even kill Cats, who in most environments are Apex Predators themselves. They are also kleptomaniacs known to steal anything Shiny such as Pots and Silverware.

Tamatoa not only mentions sunken Pirate Ships in his song Shiny, but he collects and hoards treasure, he has panache, and he can throw claws with a Demigod
(Actually Maui is a Kapua, Disney translated it to mean Demigod but that doesn't quite cover exactly what they are. It's not that they are Half Human/Half God, they are more like...powerful Supernatural Entities that represent aspects of of Nature, but also exhibit Human-like Behavior. There are 4 Major gods in the Hawaiian Pantheon: Kū, Kāne, Lono, and Kanaloa, and then there are minor gods that include Maui and Pele, probably the most famous Hawaiian gods.)
So I think he would make a pretty Awesome Pirate Captain if he had a crew.

I made Tamatoa a SHINY Crustle, although you can't really tell he's shiny while he's in his Blacklight Bioluminescent form. I imagine he has an army of other Crab Pokemon he keeps under control by being gargantuan, incredibly strong, and ruthless. It's said that he ate his own grandma, and he will also eat crew members who fall out of line.