In Mark 8:33 Jesus wasn,t saying that Peter was Satan, but was referring to the fact that Satan had inspired Peter's to say what he did.  This type of metaphor was used when God spoke to the serpent in the garden of Eden (Genesis 3:15). The serpent was merely a vehicle of communication Satan used to tempt Adam and Eve, while Peter was the vehicle Satan used to tempt Jesus. 

Ephesians 6:12 reveals that our warfare isn't with people, but against the spiritual powers who inspire and use people.  Jesus recognized that Peter's reaction to His prophecy about His death was motivated by His enemy, so He went right to the source.

Every Christian is at war.  Our enemy goes about as a roaring lion, seeking whom he may devour (1 Peter 5:8). Those who resist the devil will see him flee (James 4:7).

Some of us believe that anger will put others in their place. But "the wrath of man does not work the righteousness of God" (James 1:20).  Anger against people makes us play right into the hand of the devil. The way to overcome the spiritual powers that come against us through people is to turn the other cheek (Mattnew 5:39). This makes the demons flee in terror. We cannot win a spiritual battle with carnal weapons. We must realize who the real enemy is and fight with the spiritual weapons the Lord has given us.  It is supposed by many that the higher levels of the devil's spiritual authority takes more power to rebuke or remove.  That's not true. There is no demonic power, including the devil himself, that will not flee at the name of Jesus when faith is put in that name.  

What a wonderful name!