grammar - What does なる mean in these cases?

I'm not sure if these two have the same meaning, but I don't think they bear the meaning that I know which is the basic なる (to become).

1. 
   

   内なる声と言いますか・・

   
   


2. 
   

   彼女よりさらに深遠の、未知なる人物こそが黒幕なのではないかと疑わせるのだ…。

   
   

Answer

This なる is a form of the old copula なり (equivalent to modern だ), and specifically an earlier form of the usage that became the modern な particle used with adjectives. There are a few adjectives that can still take なる instead of な in modern Japanese; this form generally has a literary or poetic-sounding effect.

In the case of the specific two adjectives used here, 内 and 未知, the なる form is actually the only form they can take as な-adjectives in modern Japanese - 内なXX and 未知なXX aren't really used. However, they can be used regularly as noun forms, so 未知なるXX could be rephrased as the equivalent but less poetic-sounding 未知のXX, and 内なるXX similarly as 内のXX (though in the latter case it's perhaps not the most natural expression).