Peter -- born Simon, son of Jonah -- one of Jesus's disciples, is one of the Bible's most important figures. He was, according to three of the four Gospels, the first man called by Jesus to be a disciple, and he is clearly identified by Jesus as the leader of the group. His name, given to him by Jesus, is from the Greek word for "rock," which Jesus explains by saying "upon this rock I will build my church." He would go on to be one of the founders and patriarchs of the early Christian church, and is regarded by Catholics as the first pope.
When he is mentioned in the Gospels, Peter ordinarily symbolizes faith. On a spiritual level, Peter represents "truth from good," or true principles that are centered on the purpose of being good and doing what is good. In its highest state, this would be divine truth, ideas of love expressed directly by the Lord; in its lowest state it would be rules for life that need to be accepted and obeyed. The reason this is such a key concept -- and that Peter is such a crucial figure -- is that truth of this kind is the first thing we need to begin a spiritual journey to the Lord. At such an early stage we are burdened with desires for evil and can't trust our feelings and emotional reactions, but we can raise our minds above those desires and recognize the truth about the Lord and life. That way we can compel ourselves to do what is right and fight the desires to do evil; if we do that with commitment, trust, and hope in the Lord, He will slowly remove those evil desires until we become angelic, doing what's good out of love. But it all has to start with Peter -- the solid, unmoveable stone of truth that is the only worthy foundation for life.
