Legendary Birds

The Legendary Birds contain Articuno, Zapdos, and Moltres in the team.

It is shown in the second pokemon movie, Pokemon 2000: The Power of One , that if the three began to fight each other, Lugia, the trio master who rise and stop them, but it would need the help of the Chosen One, who turned out to be Ash Ketchum.

You can find Moltres in the Kanto Pokmon Championship, while in the GBA game you can find Moltres in either Victory Road or on One Island. While Articuno is where Ash is with the photographer friend of his, while in the game it is in Seafoam Islands. While Zapdos is found during Season 5 near a pond, while in the game you can find Zapdos in the Powerplant of Kanto.

In the anime
They can be seen with Lugia in Pokemon: The Power of One

Trivia

 * Their names consist of the first three spanish numbers, Articuno, Zapdos, and Moltres. Their National Pokedex numbers go in order from uno to tres, and they are the THREE legendary birds, so it makes logical sense.