The_Four_Tapus

The guardian deities (Japanese: 守り神 guardian deity) are Pokémon in the Alola region who protect the islands where they live. Each of the four main islands in Alola has a guardian deity: Tapu Koko on Melemele Island, Tapu Lele on Akala Island, Tapu Bulu on Ula'ula Island, and Tapu Fini on Poni Island. The Island Kahunas are each chosen by their island's guardian deity.
They are also referred to as the tapu (Japanese: カプ kapu), the guardians (Japanese: 守り神 guardian deity), the sacred guardians (Japanese: 守り神 guardian deity), the island guardians (Japanese: 島の守り神 island's guardian deity), the spirit guardians (Japanese: 守り神 guardian deity), the land spirits (Japanese: とちがみポケモン Land Spirit Pokémon), or the guardian tapu (Japanese: 島の守り神　カプ island's guardian deity kapu).
The guardian deities are known to take part in battles to decide who is the strongest of them all, and this inspired humans to create the Battle Royal format. They share the signature move Nature's Madness and its corresponding Z-Move Guardian of Alola.

Among the guardian deities, Tapu Koko plays the largest role within the games' storyline, appearing before the player picks their starter Pokémon to save them after they fall from a broken bridge with Nebby in tow. Tapu Koko, in recognition of the player's bravery, gives the player a Sparkling Stone, which is later refined by Hala into a Z-Ring. Tapu Koko later appears to defend Melemele Island against the then-unidentified Ultra Beast Buzzwole/Pheromosa alongside Hala. After becoming Champion, the player and Lillie visit Tapu Koko at the Ruins of Conflict to give thanks to it, after which the player battles it.
Tapu Fini, while not physically seen, plays a small role in the story as well, granting Hapu the title of Island Kahuna after her grandfather, the previous Kahuna, passed away.

The Tapus belong to Nintendo and Game Freak!

Yellow text: Tapu Koko
Pink text: Tapu Lele
Green text: Tapu Bulu
Blue text: Tapu Fini