Board Thread:Off-topic Discussion/@comment-4972558-20190524135347/@comment-5932670-20190602161303

They based Hydreigon off King Ghidorah, who is based of the Yamata no Orocho, which fits Ghetsis’ morality perfectly.

I think this is why Game Freak decided to make Hydreigon Ghetsis’ ace instead of the Champion like they did with previous champions, even if they aren’t the ace Pokémon.