What is a noun for a person who is underrated despite being really good at something? [closed]

I've always like the phrase Unsung hero for someone who's contribution is underrated/valued:

Unsung hero: a person who makes a substantive yet unrecognized contribution; a person whose bravery is unknown or unacknowledged


It depends what you mean by "somehow" underrated, but I would refer to somebody like that as a dark horse

a person who keeps their interests and ideas secret, especially someone who has a surprising ability or skill:

Anna's such a dark horse - I had no idea she'd published a novel.

It's marked as British English, so may not be known in the US.