Master Trainers (Japanese: マスタートレーナー Master Trainer) are Trainers that appear in Pokémon: Let's Go, Pikachu! and Let's Go, Eevee!. These trainers each specialize in training only one of the original 151 Pokémon, holding the title of Species Master. To challenge them for the title, players must battle the Master Trainers with the same species of Pokémon as them.They can be encountered in various locations around Kanto after becoming Champion. Master Trainers wear red clothing and have the icon of their favorite Pokémon in a bubble above their heads. Their Pokémon are high leveled and tend to have a lot of AVS and maximum IVs in certain stats.
The Master Trainers for Legendary Pokémon, Mythical Pokémon, and Ditto do not battle the player. Instead, they grant the player their title upon showing them a Pokémon of their respective specialty with a high enough CP. These Trainers all have the appearance of a Master Trainer Scientist.
Defeating at least six Master Trainers allows the player to battle Red outside the Pokémon League at Indigo Plateau, who will grant the player the title of Battle Master after being defeated. Earning every Master Trainer title, except for those of Mythical Pokémon, earns the player the title of Grand Master.
- The Jigglypuff Master, Lass Marge, takes the place of Pewter City's Pokémon Center Jigglypuff NPC from the previous games. The Jigglypuff has been relocated to the Route 4 Pokémon Center.
- The Onix of the Onix Master, Hiker Jim, knows Wrap, which Onix cannot legitimately learn.
- The English names of the Zubat and Golbat Master Trainers, West and Keaton, are references to Adam West and Michael Keaton, both of whom have played the role of Batman.