In the context of this artwork, explain the Saint Peter of the Subject.
The figure on the left in El Greco's Saint Peter and Saint Paul can be identified as Saint Peter.  In the Bible, Peter is one of the first disciples that Jesus calls upon.  In the Book of Matthew, Jesus said to Peter, “And I tell you that you are Peter, and on this rock I will build my church, and the gates of Hades will not overcome it.  I will give you the keys of the kingdom of heaven; whatever you bind on earth will be bound in heaven, and whatever you loose on earth will be loosed in heaven."  El Greco included the keys of heaven in this painting, as seen in the left hand of Peter.
Bible Paul El Greco Jesus Book of Matthew left keys of heaven Peter Saint Peter