in like episode 5 of Pokemon from 1999, Ash and everyone go into this lighthouse and meet this guy who's meant to be a top researcher of Pokemon. He basically devotes his whole entire life to studying Pokemon and finding every one there is. Even when they meet him he was researching fossils.
He starts telling them about this super rare, legendary, magical Pokemon he heard of, and most of this episode is basically him telling stories about this Pokemon and how his number one goal in life is to actually meet it one day. He said he once heard a weird cry from across the sea which he believes is by that Pokemon which he recorded and said the recording is the best thing he owns. They walk around the lighthouse for ages talking about this legend until they finally get to the top and he plays the recording he got. He say's something like "This Pokemon is one of a kind, no1 in the world has ever seen it, this recording is the only proof that it even exists". He even say's that it has no family and it wonders the sea alone because there are no other Pokemon of it's kind. Then he heard the same voice replying to the recording from across the see, and the Pokemon approaches the lighthouse and it turns out it was just a Dragonite.