Isaiah 44:6

כֹּה אָמַר ה' מֶלֶךְ יִשְׂרָאֵל וְגֹאֲלוֹ ה' צְבָקוֹת אֲנִי רִאשׁוֹן וַאֲנִי אַחֲרוֹן וּמִבַּלְעָדַי אֵין אֱלֹקים

Thus says Hashem, the King of Israel and their Redeemer, the L-rd of hosts: I am first and I am last; beside Me there is no god.

Another of the verses of Malkiyos recited on Rosh Hashana, the ibn Ezra explains this verse as follows: G-d is the exclusive “King of Israel” when they are in their land and not subject to any foreign power subjugating them. He is “their Redeemer” when they are in exile. At all times, He is “L-rd of hosts,” the hosts of Heaven testifying to His role as King.