The devil is human nature in opposition to God...
It is convenient to blame temptation on an external agent, a supernatural devil but, though the devil is sometimes personified in Scripture, it is a term for the tendencies to sin in human nature. In his death at the end of a completely sinless life, Jesus conquered completely that tendency to sin and made a way of escape for others who would associate with him.
James 1:13-15
Let no man say when he is tempted, I am tempted of God: for God cannot be tempted with evil, neither tempteth he any man: But every man is tempted, when he is drawn away of his own lust, and enticed. Then when lust hath conceived, it bringeth forth sin: and sin, when it is finished, bringeth forth death.
Hebrews 2:14-15
Forasmuch then as the children are partakers of flesh and blood, he also himself likewise took part of the same; that through death he might destroy him that had the power of death, that is, the devil; And deliver them who through fear of death were all their lifetime subject to bondage.