The Twelve Apostles (Greek:Ἀπόστολος, apostolos, "someone sent out", e.g. with a message or as a elegate) were, according to the Synoptic Gospels (i.e., the Gospels of Matthew, Mark and Luke) and Christian tradition, disciples (followers) whom Jesus of Nazareth had chosen, named, and trained in order to send them on a specific mission. After the Apostle Judas Iscariot had betrayed Jesus, the remaining Apostles under the leadership of Simon Peter filled the vacancy by electing by lot Matthias, a companion of theirs ever since they themselves had followed Jesus, so that by the time of the coming of the Holy Spirit at Pentecost they actually numbered twelve again.