Ho-Oh was shown at the end of the first Pokémon anime episode before its debut in a Pokémon video game. Ash sees the mysterious rainbow-colored Pokémon flying above him after the opening adventure with Pikachu.
At the time of the episode's Japanese broadcast on April 1, 1997, Ho-Oh was not part of the original Pokémon Red and Green games. Its appearance acted as an intriguing glimpse of an unknown Pokémon and became one of the anime's earliest mysteries.
Ho-Oh later became a central Legendary Pokémon in Pokémon Gold and Silver, which were released in Japan in 1999. It appears on the cover of Pokémon Gold, while Lugia appears on the cover of Pokémon Silver. Fans sometimes identify the bird in the first episode as Moltres because of its fiery appearance, but the episode's unidentified rainbow Pokémon was Ho-Oh. The scene helped link the anime to the expanding game universe.