Ho-Oh appears briefly in the first episode of the Pokémon anime before Ash reaches Viridian City.
Near the end of “Pokémon, I Choose You!”, Ash looks up and sees a large, colorful bird Pokémon flying across the sky. At the time, Ho-Oh had not been revealed as part of the original game’s known Pokédex, making the scene a memorable mystery for viewers.
Ho-Oh was later identified as a Legendary Pokémon associated with Pokémon Gold and Silver. Its early anime appearance therefore acted as a preview of a Pokémon from the franchise’s next generation. The moment also helped establish that the anime could show creatures beyond the species immediately familiar from the first games.
Ho-Oh is often confused with the first-generation Legendary birds Articuno, Zapdos, and Moltres. Those three are part of the original Kanto Pokédex, whereas Ho-Oh is a Johto Pokémon. The bird in the opening episode is specifically Ho-Oh, not one of Kanto’s Legendary trio.