Tamatoa is a gargantuan coconut crab that hails from Lalotai, a realm inhabited by monsters. Living in a giant seashell within the realm's depths, Tamatoa loves all things shiny - his shell is covered in gold, artifacts and treasures as indication of this. He is an avid collector and hoarder, and his materialistic obsession has driven him into madness over time.
Tamatoa is also the longstanding arch-nemesis of acclaimed demigod Maui. The two appear to know each other extremely well, with Tamatoa even having knowledge of Maui's near-tragic beginnings. During one of their battles, Maui ripped off Tamatoa's leg which, according to Maui, plays a part in the giant crab's hatred for him. Despite his own physically prowess, Tamatoa fears Maui and Eric when the latter are equipped with his magical fish hook, Seablade, and Fist of Zeus.
Tamatoa is unpredictable and possibly insane. His mood tends to shift at the drop of a hat, going from cheeky and comedic, to murderous and menacing in a mere matter of seconds. He's quite monstrous in both size and attitude, one of his most well-known traits being his sadistic habit of eating anyone around him, be they humans, sea creatures or even gods—he even admitted to eating his own grandmother.
Tamatoa also has a twisted sense of humor, specifically shown when he nonchalantly commented that it took a week to eat his grandmother and blamed the delay on her enormous size in a dry tone. He also takes pleasure in torturing his enemies both mentally and physically, as shown when he playfully - yet brutally - thrashed Maui across his lair, while crushing the demigod's ego at the same time. With an apparent lack of boundaries, Tamatoa has no qualms with mocking someone's dead loved one, or exposing someone's deepest insecurities to amuse himself.
Above all, Tamatoa is extremely narcissistic. With a superiority complex, he views himself as beautiful, and others as irrelevant and disposable. This is only surface-level, however, which actually serves as an antithesis between Tamatoa and the film's overarching message of identity and being true to yourself: Unlike Moana, Tala and Maui, Tamatoa does not believe in inner-beauty or "listening to your heart". Instead, he views anyone who is not physically attractive or outwardly strong as insignificant and lesser than him, albeit perfectly fit for a meal. This is his biggest flaw and ultimately causes his downfall, as he underestimated Moana's intelligence (because she's a human), which allowed her to best the villainous crustacean. Though he considers himself beautiful, however, he welcomes anything that will increase his power and, by extension, his social status, such as the heart of Te Fiti.