Though his identity is not mentioned in so many words yet (it’s finally explicitly stated in Revelation 4:8), it is very clear that this is God almighty. The Old Testament had repeatedly mentioned that the Lord God has established his throne in the heavens (Psalm 11:4; Psalm 47:9; Psalm 93:2; Psalm 103:19). In fact, the Most Holy Place of the tabernacle was a throne room, with God enthroned on the mercy seat on the ark (Exodus 25:1–40; 1 Samuel 4:4; 2 Samuel 6:2; 2 Kings 19:15).
2 At once I was in the Spirit, and behold, a throne stood in heaven, with one seated on the throne.