Naturals

a natural ~
生まれながらの

Example:
He's a natural soccer-player.
彼は生まれながらのサッカー選手だぜ。

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have a talent for
の才能がある

Example:
She has some real talent for the piano.
彼女は本当にピアノの才能があるね。

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have a knack for
の才がある

Example:
You've got a knack for learning languages.
君は語学の才があるよ.

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Comment:
I think the strength of the expression goes from top to bottom; that is, a natural probably has the most ability, followed by a talented person, and someone with a knack probably has the least ability of the three. But they're all still high compliments.