star performer; leading player; box-office draw
Originally from theater, referring to the single main attraction or star whose name is on the signboard. Now used for any field's standout performer.
He is the star performer of this theater company.
That singer is active as the agency's leading star.
one's best asset; sole strong point; trump card
Extended figurative use: the one thing or person you can proudly show off, often implying it's the only notable asset.
This dish is our restaurant's signature item.
His one strong point is his English ability.