https://www.polygon.com/2018/11/7/18072704/pokemon-lets-go-trailer-red-blue-green-trainer-fights

Pokémon: Let’s Go! stays largely faithful to the original Red, Blue, and Yellow — with some noted twists — but its historical nods to the series stretch even farther back. The game’s latest trailer, likely the last ahead of launch, reveals that the trainers Red and Blue appear, joined by fellow trainer Green for the first time.

Red and Blue are canonical Pokémon masters of the Kanto region, with Blue standing as the most familiar to fans. Otherwise known as Gary Oak, he’s the grandson of Professor Oak and one of the strongest trainers players fight against in the first-gen games. Meanwhile, Red is the default name for the character that players assume in Red/Blue/Yellow, but he also shows up as a rival trainer in Silver/Gold/Crystal. He’s the toughest trainer a player will face in the second generation, and usually the last challenge players undertake before finishing the game.