Super-ancient Pokémon

The weather trio is, for lack of a better defining characteristic of the three, the name of the legendary trio made up of Groudon, Kyogre, and Rayquaza.

Although several non-legendary Pokémon, notably Tyranitar and Yukinooh, have abilities that can alter the weather conditions, and the Golduck family is capable of having an ability that can stop them altogether, Groudon, Kyogre, and Rayquaza's abilities were the first sight of these weather-changing ones in the games.

Unlike Pokémon with moves like Sunny Day and Rain Dance, where the weather changes to another for only five turns, the abilities of the legendary trio cause their weather effect for the remainder of the battle, or until the weather is changed again in some way. Rayquaza's, however, only lasts as long as it remains active, and removes the effects of any weather on the field, leaving it to just be a pretty effect.