Charizard was the first Pokémon shown in the original Japanese Pokémon anime opening sequence.
The opening theme accompanied the anime’s debut in Japan in 1997 and quickly became one of the franchise’s most recognizable pieces of music. Charizard appears prominently at the beginning of the sequence before the opening montage introduces other Pokémon and characters.
This fact is separate from the anime’s main protagonist: Ash’s partner is Pikachu, but Pikachu is not the first Pokémon shown in that particular opening image. The opening also should not be confused with later regional or English-language edits.
Charizard’s prominent placement reflects its importance in the first-generation games and anime. It was the final evolution of Charmander and became one of the most recognizable Pokémon in the franchise’s early years.