From Bulbapedia, the community-driven Pokémon encyclopedia.
The ancient Protectors chief and council
The modern descedants of the Protectors, including Ridley
The Protectors are an ancient society from Unova, which is responsible for protecting Meloetta.
The Protectors' civilization once lived on what is now the Abyssal Ruins. However, Meloetta sunk their city to the bottom of Undella Bay in ancient times after greedy people wanted to use its power to control the Forces of Nature and the world. While much of the society went down with the city, the remnants relocated to a hidden valley on the Unova mainland so they could continue protecting Meloetta from ill-intentioned people. The descendants are incredibly close to Meloetta and even have the ability to hear its voice across large distances.
Prior to An Epic Defense Force!, the Team Rocket trio captured Meloetta, and Ridley immediately left the village to relocate the Mythical Pokemon. Meloetta later escaped the trio's clutches and soon befriended Ash and his friends.
In Meloetta and the Undersea Temple!, Ridley was flying on his Golurk when he heard Meloetta's song and tracked it to Cynthia's villa in Undella Town. However, the reunion was short-lived when the Team Rocket organization, bolstered by the arrival of Giovanni, captured Meloetta once again and used its voice to raise the Abyssal Ruins from the sea and summon the Forces of Nature. With the assistance of Cynthia and Ash's group, Ridley was able to disrupt Team Rocket's Operation Tempest, soothe the aggressive Forces of Nature, and rescue Meloetta by the end of Unova's Survival Crisis!. Afterwards, Ridley and Meloetta returned to their hidden homeland.