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. Ho-Oh, on the other hand, does not take an active role in its trio, instead being responsible for their creation when the Brass Tower burned down.

The Regis as well have a master, in Regigigas. With the large distance separating the Hoenn region from Snowpoint City in Sinnoh, it is yet unknown what purpose Regigigas serves to the rest. It is possible that the ancients who found, or created, Regigigas used Regirock, Regice, and Registeel as keys to keep the powerful Pokémon from escaping, and then hid them in caves in Hoenn, sealing them away likewise with keys that could only be opened using HMs, Relicanth, and Wailord.

The lake trio may have a known master, Arceus, as it is said that Arceus created them to oversee its will in Sinnoh.