Trio master

A Pokémon that is a trio master is one who, in some way, oversees a legendary trio of Pokémon.

The trio master and the trio itself may relate in different ways. For example, Lugia is the trio master of the legendary birds; it is the only one who can quell their fighting when Lawrence III captures one of them in The Power of One.

In the games, the trio master sometimes will and sometimes will not require that the members of its legendary trio be captured beforehand. In Crystal, Ho-Oh cannot be captured until all three of the legendary beasts have been, and in Diamond, Pearl, and Platinum, Regigigas will not awaken unless the player has the legendary golems in his or her party. Lugia and Arceus, however, do not seem to have this requirement, nor does Ho-Oh in Gold and Silver and Rayquaza in the Generation III games. However, in Pokémon Mystery Dungeon, the legendary birds must all be befriended before the player can enter Lugia's dungeon, and before encountering Ho-Oh, the three legendary beasts must contribute their power to create the Rainbow Wing. In order to get Ho-Oh in Pokémon Colosseum, the player must first capture and purify all the Shadow Pokémon, which includes the legendary beasts, as one of the two requirements.

Trio masters' relation to their trio

Trio master	Legendary trio
	Relationship with the master
Lugia	Articuno	Zapdos	Moltres
	Lugia is the only one who can end the legendary birds' fight, as seen in the second movie.
Ho-Oh	Raikou	Entei	Suicune
	After the three Pokémon perished in the fire at the Brass Tower, Ho-Oh revived them.
Rayquaza	Groudon	Kyogre	Rayquaza
	Due to it ending the other two members' fight in Emerald, Rayquaza may internally be the master of the weather trio.
Regigigas	Regirock	Regice	Registeel
	Regigigas will awaken when the three legendary golems are brought to its residence. It is also said that it built statues made of rocks, ice and magma.
Arceus	Dialga	Palkia	Giratina
	According to legend, Arceus created all three members of the dragon trio.
	Uxie	Mesprit	Azelf
	Arceus also created the lake trio, making Arceus the only trio master that is related to more than one legendary trio.