RED ASH
Well... First of all, they originate from the same place and world.
The Pokemon world...
Ash stars in the anime series
And Red is the character in the Pokemon video games
The only thing that's different from them two, is their personality.
- Red is a Pokemon Master while Ash isn't even close to being one.
- Red travels alone while Ash needs a boy and a girl traveling with him.
- Red destroyed the Team Rocket organization by himself while Ash has never ending bickering with Jessie and James from Team Rocket...
This theory I have researched is a little different than expected, but it goes with both the anime series and video game.
SOOO! The story starts with Ash's parents getting divorced... which is pretty obvious since Ash never had a dad in the series. One day... Ash, his mom, and his brother were driving home one day. OKAY! For people who are wondering, Red is Ash's brother in this theory... OKAY WITH IT?
So anyways, they were driving home and Ash didn't put his seat belt on. And BOOM! The car crashed... And Ash got brain damage. So he was now a little disabled...
So Red got worried as he started off on his journey. So he went to his first gym... the Pewter Gym. And when he beats Brock, the gym leader, he goes up to him and asks him if he could travel with Ash when he became a trainer. And Brock agrees and Red moves on.
So as you know, Blue is Red's rival. And Blue is basically Gary because Blue and Gary have too much in common to not be the same person. And Blue always teases Ash making Red and Blue rivals. So one day, Red comes up to Blue and asks him to be Ash's rival when he goes on his journey. And he accepts.
So Red keeps traveling for about 3 years and realizes something. Ash is gonna start his journey soon. So Red makes a final attempt to help Ash and sends his Pikachu to Professor Oak so he could give it to Ash. This explains why Pikachu didn't like Ash at first. It also explains why Ash's Pikachu is so strong at first.
Red reaches a mountain called Mt. Silver. So Red decides to train there.
People say he died on the mountain. So I don't know the whole theory...
And they also say that Ash had to battle Red's ghost. And when you beat him, he feels complete and disappears and goes to Heaven.