Christian Apostles stems from how Jesus, in the Gospels, selected Twelve Apostles. Currently, major missionaries are called apostles.
Jesus is stated in the Gospels to have selected Twelve Apostles. After his resurrection, Jesus sent eleven of them (minus Judas Iscariot) by the Great Commission to spread his teachings to all nations. There is also an Eastern Christian tradition derived from the Gospel of Luke of Seventy Apostles. Paul the Apostle (Saul of Tarsus), not one of the Twelve or the Seventy but a later convert, 'the apostle of the Gentiles', [Romans 11:13] claimed a special commission from the resurrected Jesus, separate from the Great Commission given to the eleven. Paul did not restrict the term apostle to the Twelve, referring to his mentor Barnabas and others as apostles, either because he didn't know it or resisted it. This restricted usage appears in Revelation. In modern usage, major missionaries are sometimes termed apostles, as in Saint Patrick, 'Apostle of Ireland'.