The Catholic Church, also known as the Roman Catholic Church, is the largest Christian church, with more than 1.2 billion members worldwide. It is among the oldest religious institutions in the world, and has played a prominent role in the history of Western civilisation. The Catholic hierarchy is headed by the Bishop of Rome, known as the Pope. The Catholic Church teaches that it is the one true church founded by Jesus Christ, that its bishops are the successors of Christ's apostles and that the Pope is the sole successor to Saint Peter, who has primacy among the apostles. The Church maintains that the doctrine on faith and morals that it presents as definitive is infallible. The Catholic Church is Trinitarian and defines its mission as spreading the Gospel of Jesus Christ, administering the sacraments and exercising charity. Its principal doctrines are found in the Nicene Creed. Worship is highly liturgical, focussing on the Mass in which the sacrament of the Eucharist is offered as a sacrifice for sin. The Church teaches that through Eucharistic consecration bread and wine become the body and blood of Christ, a change it calls transubstantiation.