Hala

Hala is the grandfather of Hau and the kahuna of Melemele Island. He specializes in Fighting-type Pokémon and grants the Melemele stamp to Trainers who defeat him. In Sun and Moon, he also becomes a member of the Alola Elite Four.

As revealed in League Offenders and Defenders! (SM128), Hala was once Professor Kukui and Guzma's mentor. He attempted to keep the peace between the pair, but Guzma became disillusioned with Hala's teachings and decided to become strong on his own without using a Z-Ring or Z-Crystals.

(Source: Bulbapedia)