Thus saith Cyrus king of Persia: All the kingdoms of the earth hath the LORD, the God of heaven, given me; and He hath charged me to build Him a house in Jerusalem, which is in Judah. Whosoever there is among you of all His people--the LORD his God be with him--let him go up.

—2 Chronicles 36:23 (JPS)

Here, Cyrus seems to believe that God (the god of the Jews) has the power to give him all kingdom in the earth. Does Cyrus in fact believe in God?

Note: I deliberately put YHWH there because the question is whether Cyrus think that YHWH, God of Israel, has power over the whole world and because that's what the original hebrew text says.

If Cyrus says, the LORD, has given me all countries, well, it could be other LORD. Cyrus, from Persia, is probably monotheistic too believing in monotheistic Ahura Mazda, for example, or his own supreme pantheon. The word, the LORD for Cyrus, could mean his own monotheistic God.

The LORD, while mean YHWH to christians and jews, do not necessarily mean YHWH for Cyrus. It's to make the question clearer and in no way meant to insult God.