They're often referred to as the 12 apostles as well because according to Christian beliefs, between the resurrection and the ascension of Jesus, he tells the apostles, look, go spread the word. Apostle comes from Greek for the one who spreads the word. These were the first Christian missionaries. Now, first amongst these apostles is often considered Peter. This is Peter right over here. He is mentioned in the gospels. He is beside Jesus at the time of the transfiguration.