is,

The sinful man; the old you that existed before you became born again.
(See more at: 'Dead', 'Dead to Sins', Crucified', and 'Mortify'.)

Knowing this, that our old man is crucified with him, that the body of sin might be destroyed, that henceforth we should not serve sin. For he that is dead is freed from sin.
Romans 6:6-7