奴なんだ

is the one/person

→ 奴
phrase Uncommon #16,457
is the one/person A casual explanatory expression meaning that someone or something is the person or thing being referred to. 奴 (やつ) can mean “guy,” “person,” or “thing,” depending on context.
JA: あの人が探していた奴なんだ。
EN: That's the person they were looking for.

俺にとって兄貴みたいな奴なんだ

He's like an older brother to me.

— シティ・オブ・ゴッド (2002)

植野ダメな奴なんだ

(Ueno) I'm just no good.

— 映画 聲の形 (2016)

そんな事するって、どんな奴なんだ

What kind of guy would do something like that?

彼は本当にいい奴なんだが、私は彼が好きではない

He’s a really nice guy, but I don’t like him.

トム真面目な奴なんだ

Tom is a serious guy.

トム態度がでかい奴なんだ

Tom has a really big attitude.

トムケチな奴なんだ

Tom is a cheapskate.

あんたは何て奴なんだ

What kind of person are you?

— 帰ってきたヒトラー (2015)

あいついい奴なんだ

He's a good guy.

あいつ根は優しい奴なんだ

Deep down, he's a kind person.

ルームメイトトムってすごいいい奴なんだ

My roommate Tom is a really great guy.