It is believed that Jesus, even assumed, that Jesus said this, implying he is "[Almighty] God", in turn, "The Father".
However, on the other side of the spectrum, verses Revelation 1:8, 21:6 and 22:13 identifies not Jesus, but rather, The Father Himself. This is obvious when you check out the references.
Alpha and omega are the first and last letters of the Greek alphabet. The respective positions of these letters in the Greek alphabet are used to illustrate that God [Yahweh or Jehovah in modern English] alone is the beginning and the end, which brings us to Revelation 21:6. For The Most High is Almighty God, and he will continue to be Almighty God forever and ever. He is the only one who can be noted as from everlasting to everlasting (Psalm 90:2).
The final occurrence we see in Revelation 22:13. It is evident that a number of persons are represented as speaking in this chapter of Revelation, mainly verses 8 and 9, show that the angel spoke to Apostle John. Verse 16 obviously applies to the Lord himself - Jesus, the first part of verse 17 is credited to the spirit and to the bride of the Lamb, and the one speaking in the latter part of verse 20 is manifestly John himself.
The Alpha and the Omega of verses 12-15 properly be identified as the same one who bears the title in the other two occurrences, God our Father. The expression such as Look, I am coming quickly, in verse 12, does not require that these aforementioned verses apply to Jesus, inasmuch as God also speaks of himself as coming” to execute his judgment. This can also be compared with Isaiah 26:21. In Malachi 3:1-6, it speaks of a joint coming for judgment on the part of God our Father and his Messenger of the Covenant..
Now we have Revelation 1:11 from a Textual Citric standpoint. The additional occurrence of this phrase in the King James version of Revelation 1:11 (and or any translation that shares later MSS), the reality is, it does not receive much support from some of the oldest Greek manuscripts copies that we have, including the Alexandrine, Sinaitic, and Codex Ephraemi rescriptus. It is, therefore, omitted in many modern and or revised Bible translations.
A sidenote, Jesus is the first and last of a new creation that is to come whereas the creation of God begins and it connects to God's original purpose, for example, we have the New Covenant.