Ho-Oh first appeared in the debut episode of the Pokémon anime before appearing in a game.
At the end of “Pokémon, I Choose You!”, Ash and Pikachu see a large golden bird flying above a rainbow. Ash checks the Pokédex, but it has no identifying information for the mysterious Pokémon. The creature is Ho-Oh, although the episode does not name it at that moment.
Ho-Oh later became a major Legendary Pokémon in Pokémon Gold and Silver, where it is associated with the Johto region and appears on the cover of Pokémon Gold. The games were released in Japan in 1999, after the anime premiere in 1997.
This early appearance is easy to confuse with Lugia, the cover Legendary of Pokémon Silver, or with Mewtwo, the central figure of the first movie. Ho-Oh’s brief anime cameo was an early example of the franchise showing a future Pokémon before players could encounter it in a main-series game.