Peter was the foremost among the twelve Apostles of Jesus, and one of the most influential people in spreading Christianity after the end of Jesus' earthly ministry. Peter followed and aided Jesus during His time on earth, and later went to Rome to found a church there. As the first Bishop of Rome, Peter is seen by Catholics as the first Pope. He also wrote two letters in the New Testament, 1 Peter and 2 Peter.
Peter's birth name was Simon; he was given the name Peter (meaning 'rock') or Simon-Peter by Jesus, who said 'on this rock I will found my church'. Interestingly, Peter's character as shown in the Gospels is not steady and rock-like, but somewhat mercurial: he is prone to outbursts of excited zeal and extremely strong faith, but at other times his faith falters. For example, he is briefly able to walk on water until he questions his safety and consequently falls in; and despite his unmatched devotion to Jesus he famously denies Him three times around the time of the crucifixion. In all, Jesus' calling such a man to be His 'rock' continues a tradition of God calling unlikely men to serve Him that includes Moses (an outcast and murderer), David (a shepherd-boy with no military or governing experience), and Jonah (an incorrigible coward).
The early church
After Jesus' Ascension, Peter became the leader of the disciples as they spread the Gospel and began to increase the size of the early church. Many of his deeds, including miracles of healing, are recounted in the Book of Acts. It seems that at one point, Peter came into conflict with that other great early evangelist, St Paul - see Galatians 2:11.
Peter eventually went to Rome and founded a flourishing branch of the church. As the first head of the church in Rome, Peter is seen by Catholics as the start of a continuous line of Popes that stretches back 2000 years. Like all early Popes, Peter is traditionally thought to have been martyred for his belief: the story is that his death came during the persecutions instigated by the emperor Nero. When the authorities threatened to crucify him, Peter is said to have requested that they do so upside-down, as he did not consider himself deserving of the same fate as Jesus. Consequently, an inverted Christian cross is known as a Cross of St Peter. Peter's status as first Pope is honoured by the dedication of St Peter's Basilica in the Vatican.
Peter is traditionally depicted in painting and sculpture as a brown-haired, bearded man holding a key, or sometimes two keys. These are the keys to Heaven, representing the power bestowed by Jesus in John 20:23. Further extrapolating along these lines, Peter is often thought to sit at the gate of Heaven, and is shown there (or specifically at the gate of Purgatory, which eventually leads to Heaven for all who enter) in Dante's Divine Comedy.