the uncrowned king/queen
the uncrowned king/queen of (something)
Someone popularly considered to be the best or most impressive in a particular field or activity. The young woman has attracted a huge and fervent fan base, with many calling her the uncrowned queen of social media. In my opinion, he's not just the uncrowned king of featherweight boxers, but the best fighter in the entirety of the sport.
(be) the ˌuncrowned ˈking/ˈqueen (of something)the person considered to be the best, most famous or successful in a particular place or area of activity: Because of her expertise, she is regarded as the uncrowned queen of music in Pakistan.
A king or queen who is uncrowned, has not yet had a crown placed on their head.