Ho-Oh first appeared unidentified above Ash and Pikachu at the end of the Pokémon anime’s first episode. The episode is titled “Pokémon, I Choose You!” and originally aired in Japan in 1997.
After Ash leaves Pallet Town, he and Pikachu encounter a flock of angry Spearow. Following the encounter, Ash sees a large, colorful Pokémon flying through the sky and later notices a rainbow. At that point, the character and audience are not told the Pokémon’s name.
Ho-Oh was not introduced as a playable species until Pokémon Gold and Silver, the second-generation games. Its early anime appearance therefore became a notable mystery for viewers familiar only with the first-generation games. The Pokémon’s identity was eventually established as Ho-Oh, a Legendary Pokémon associated with rainbows and resurrection.
A common mix-up is to identify the flying Pokémon as Lugia, because Lugia is also a prominent Legendary Pokémon from the second generation. Lugia, however, is strongly associated with the second Pokémon movie, while Ho-Oh is the mysterious figure shown in the anime’s opening episode.