Mark was an Evangelist—one of the four men who wrote the Gospels found in the New Testament. Mark’s Gospel was written first, and it is the shortest description of Jesus’ life, Death, Resurrection, and Ascension. Mark’s writings helped both Matthew and Luke to write their Gospels.
Luke was an Evangelist, the writer of the third Gospel. He never met Christ in person, but in his Gospel he says that he came to know about Jesus by talking to eyewitnesses to the events of Jesus’ life, death, and Resurrection. Hearing those stories helped Luke to become a believer, and he wrote his Gospel so that others would come to know and love Jesus.
John is sometimes called “the beloved disciple” or “John the Evangelist.” He was the only one of Jesus’ apostles who did not leave him during his crucifixion and death. In the Gospel Jesus even asks John to take care of Mary, the Blessed Mother, after his death.