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.

Trio Masters and Their Underlings

---

Legendary Bird Master: Lugia
Lugia's Underlings:
Articuno
Zapdos
Moltres
Relation to Underlings Lugia is said to be the only Pokemon capable of stopping the Birds from rampaging.

Legendary Beast Master: Ho-oh
Ho-oh's Underlings:
Raikou
Entei
Suicune
Relation to Underlings
Ho-oh took pity on the Beasts after they perished in the Brass Tower fire, and revived them. As such, the Beasts follow Ho-oh's orders, although Suicune is significantly more free-spirited than Entei and Raikou.

Legendary Golem Master: Regigigas
Regigigas's Underlings:
Regirock
Regice
Registeel
Relation to Underlings
The relation between Regigigas and the Golems is disputed. Some believe that the Golems were made, or found, by the same people who made/found Regigigas, in an attempt to seal Regigigas away for some reason. Then, the golems were sealed away as well, in order to more effectively secure Regigigas in its tomb. This makes sense, as Ruby and Sapphire take place before Diamond and Pearl, and since the Golems would be released at this point, it is logical to believe that the seal on Regigigas would be broken when the revived Golems come into close contact to its temple.

Legendary Pixie Master: Arceus
Arceus's Underlings:
Uxie
Mesprit
Azelf
Relation to Underlings
Arceus created these three Pokemon to create the souls of living creatures, bestowing Knowledge, Emotions, and Courage.
Although it is widely accepted that Arceus is the master of the Pixies, there is still some debate about Arceus's connection to the Pixies. Some people believe that Arceus is not the Pixie's master, but in fact is the master of Dialga, Palkia, and Giratina, as Arceus is said to have cloned itself into Dialga and Palkia, and as a result, Giratina was made. This would make it closer to these three dragons than to the Pixies, and would be the first time a trio of Uber ranked Pokemon had a master.