The Son of man is a messianic title from Daniel 7:13, and is Jesus' favorite designation for Himself.

Revelation 1:18 - I am he that liveth, and was dead; and, behold, I am alive for evermore, Amen; and have the keys of hell and of death.

Christ is the living God, so Christ is he that liveth. He also became dead when he humbled himself to die on the cross (cf. Phil. 2:6-8), but then rose to live forevermore. So it refers to Jesus.

Love,
Madeline