Kilton

In BotW, Kilton ran the Fang and Bone shop, a place where Link could buy unique gear made out of monster parts in exchange for a special currency called Mon.

In Tears of the Kingdom, Kilton comes back, but this time is his brother Kolton who'll be running a special shop of his own.

To this character, go to the beach just north of Pico Pond in Eldin, close to the Woodland Stable. Kilton will be standing outside the Pico Pond Cave's entrance (coordinates 1208, 1214, 0020). Talk to him so Kolton comes out of the cave, which starts the side quest "The Hunt for Bubbul Gems!"