Refers to Jehovah. Comp. 22:13. The following comments from the Hebrew Daily Prayer Book, p. 3, are pertinent:
"He is the Lord of the universe, who reigned ere any creature yet was formed: At the time when all things were made by his desire, then was his name proclaimed king. And after all things shall have had an end, he alone, the dreaded one, shall reign Who was, who is, and who will be in glory."
Only, there will never be a time when all things shall have an end in the sense that they shall no longer exist. "Of the increase of his government and peace there shall be no end." (Is. 9:7)