Peter, saint or satan?

Matthew 16:23
But he turned, and said unto Peter, Get thee behind me, Satan: thou art an offence unto me: for thou savourest not the things that be of God, but those that be of men.

Mark 8:33
But when he had turned about and looked on his disciples, he rebuked Peter, saying, Get thee behind me, Satan: for thou savourest not the things that be of God, but the things that be of men.

Luke 4:8
And Jesus answered and said unto him, Get thee behind me, Satan: for it is written, Thou shalt worship the Lord thy God, and him only shalt thou serve.

Peter was one of the 12 disciples of Jesus.  Full name is Simon Peter, son of Jona.  Catholics thinks highly of Peter.  They consider him a saint, thus St. Peter or Saint Peter.  As many of you probably notice, there are a lots of catholic churches and private schools named after St. Peter.  Peter, the fisherman, was the one who denied Jesus 3 times according to the Bible (Luke 22:54-62)

But according to the 3 verses above, Jesus called him Satan.  

Here's something more interesting, he commanded his disciples not to tell anyone that he was Jesus Christ.  (Matthew 16:20)

"20 Then charged he his disciples that they should tell no man that he was Jesus the Christ."  - Matthew 16:20  KJV

What do you guys think?  or am I reading this wrong?