Ash receives Pikachu first in the Pokémon anime episode “Pokémon, I Choose You!”
Ash is supposed to choose one of Professor Oak’s three standard Kanto starter Pokémon, but he arrives late and finds Bulbasaur, Charmander, and Squirtle already claimed by other trainers. Oak gives him Pikachu instead.
Pikachu is difficult from the beginning: it refuses to stay inside its Poké Ball and does not obey Ash’s commands. Their relationship changes after Ash risks himself to protect Pikachu from attacking Spearow.
In the video games, Pikachu is not one of the three original starter choices in Pokémon Red and Green. The anime’s decision to make Pikachu Ash’s partner helped establish the character as the public face of the franchise.