Revelation 1:8

8 I am Alpha and Omega, the beginning and the ending, saith the Lord, which is, and which was, and which is to come, the Almighty.

In Revelation 1:4, the one which is, which was and which is to come was the Father but in Revelation 1:8 in the context of Revelation 1:5-8 it applies to Jesus. This is verified in verses 11-18 where we see the person speaking is clearly Jesus. This verse also implies that the Son of God always exists in the three names by which we know or will know Him. The name, "which was", is the pre-incarnate Son of God known as  "YHWH"  (literally "I am who I am"). The name, "which is", has to be the Son of God incarnated, the Savior who entered the world and died for our sins. His name in Hebrew is "Yeshua" (Joshua or Jesus in the Greek - and His name literally means, "YHWH is salvation"). The name of the Son of God, "which is to come", has a name no man yet knows when He returns in glory as King of Kings and Lord of Lords. It is the name we will know Him by for eternity.

Revelation 19:12  His eyes were as a flame of fire, and on his head were many crowns; and he had a name written, that no man knew, but he himself.

Revelation 1:8 along with Revelation 1:11-18 and many others indicates that Jesus is also Almighty God.  Jesus is the only express or exact image of the Father. This is why God will not endure any other image but Jesus to represent Himself.

Hebrews 1:3 Who being the brightness of his glory, and the  express image of his person, and upholding all things by the word of his power, when he had by himself purged our sins, sat down on the right hand of the Majesty on high;

Isaiah 9:6   For unto us a child is born, unto us a son is given: and the government shall be upon his shoulder: and his name shall be called Wonderful, Counsellor, The mighty God, The everlasting Father, The Prince of Peace.