"I am the Alpha and the Omega, the Beginning and the End," says the Lord God, "who is and who was and who is to come, the Almighty." -- World English.
It should be very obivious that this is referring to the unipersonal God of Revelation 1:1; Revelation 1:4, Revelation 4:2,8; who is, was and is to come, and who sits on the throne. Jesus is distinguished from the unipersonal God in Revelation 1:5 and again in Revelation 5:6,7.
It should also be obvious "the Lord" in the expression "the Lord God" represents Yahweh (Jehovah); evidently the Holy Name was changed to "the Lord" in this verse as it has been changed in such verses as: Matthew 4:7; 4:10; 22:37; Mark 12:30; Luke 4:8,12; 10:27; Acts 3:22; 7:37; 1 Peter 3:15; Revelation 4:8; 11:17; 15:3; 16:7; and many other places throughout the New Testament.