According to tradition, the author, Mark is not an apostle himself. Not one of the original disciples, but rather the follower of one of them. Traditionally, he's supposed to be the disciple of Peter ....

Why are Mark and Luke not apostles?

As for the other Gospels, Mark was said to be not a disciple but a companion of Peter, and Luke was a companion of Paul, who also was not a disciple. Even if they had been disciples, it would not guarantee the objectivity or truthfulness of their stories.

Is mark one of the 12 apostles?

St. Mark (first century A.D.), one of the 12 Apostles chosen by Jesus, is traditionally considered the author of the Second Gospel. Little is known of Mark as a person. He is called "John" in three of the texts of the New Testament (Acts 12:12,25; 13:5,13; 15:37).