Like people who own tons of Bitcoin or crypto but bought them without KYC? Either before KYC was a thing, or bought them through methods that did not involve KYC?
Usually whales are in a form of institution but if it's a single person, I think they buy bitcoin via OTC or over-the-counter. They find someone who sells bitcoin in their area then meet each other to do the trade.They don't go through to decentralized exchanges to buy because these DEXs' will definitely ask for some documents to withdraw that huge amount. It will also create a sudden pump on lower timeframes if they buy directly on those exchanges.