Clarifying because some people seems confused (or just salty because they like one version of the character but not the other).
Red and Ash ARE indeed the same character, it's just that it lives several different experiences in each medium. Not every version of this character has the same exact pokémon team, not every version has the same exact appearance, not even always the same names, but they are still the same character in different versions of the story. Both are skilled trainers from Pallet Town that started their journey at same time as Samuel Oak's grandson, got a Pikachu and (at least one of) the 3 starters from Kanto, they always have similar clothing and most of times, the same name (in fact, Red wasn't even called like that until GS's release, before that he was just called Satoshi, like its anime counterpart).
Basically what
>>35722653 said, they aren't the same exact individual but they are the same basic character. The guy you control in Gen 1/3 is Satoshi/Red, the guy you battle in Gen 2/4, 5 and 7 is Satoshi/Red, they guy you see in the main anime series and movies is Satoshi/Red, the protagonist of most spin offs mangas that has a Pikachu is Satoshi/Red, they guy that has a Mega-Charizard and catchs Mewtwo in that mini series is Satoshi/Red, etc.
That said, we don't know if the protagonist of Let's Go! is Satoshi/Red or not, but we'll see once the game/new info is released. If this game replaces RGBY/FRLG in the timeline then that kid is indeed Satoshi/Red, the very same guy you fought in Alola the last two games
