A.T. Robertson Commentary Revelation 1:8

"I am the Alpha and the Omega, saith the Lord God, who is and who was and who is to come, the Almighty." — Revelation 1:8 (ASV)

The Alpha and the Omega (το Αλφα κα το Ο). The first and the last letters of the Greek alphabet, each with its own neuter (grammatical gender) article. This description of the eternity of God recurs in 21:6 with the added explanation η αρχη κα το τελος (the Beginning and the End) and of Christ in 22:13 with the still further explanation ο πρωτος κα ο εσχατος (the First and the Last). This last phrase appears also in 1:17; 2:8 without το Αλφα κα το Ο. The change of speaker here is unannounced, as in 16:15; 18:20. Only here and 21:5f. is God introduced as the speaker. The eternity of God guarantees the prophecy just made.

The Lord God (Κυριος ο θεος). "The Lord the God." Common phrase in Ezekiel (Ezekiel 6:3,11; 7:2, etc.) and in this book (4:8; 11:17; 15:3; 16:7; 19:6; 21:22). See 1:4; 4:8 for the triple use of ο, etc. to express the eternity of God.

The Almighty (ο παντοκρατωρ). Late compound (πας and κρατεω), in Cretan inscription and a legal papyrus, common in LXX and Christian papyri, in N.T. only in 2 Corinthians 6:18() and Re 1:8; 4:8; 11:17; 15:3; 16:7,14; 19:6,15; 21:22.