Mew?
There are more than one, and most tend to keep to themself. With the exception of the most famous; Guildmaster Genesis
He’s believed to be the oldest, most powerful Pokemon alive, and founded the original exploration guilds. There are rumors he’s so ancient that he even coexisted with The Humans
One of his oldest claims to fame on record is putting down a feud between Groudon and Kyogre, who in the midst of their own fighting began to intrude their territories into the sky
He “united” pokemon local to the region and organized the construction of Sky Tower
At the summit of which he contacted an unaware Rayquaza, who descended and ended the confrontation
The tower itself remains in place, as well as the structures the pair had created; though the entire region is forbidden to all but the highest levels of explorers, with ascending sky tower becoming a Trial to achieve the Highest Rank