John Mark, the nephew of Barnabas, was an important figure during the Apostolic age. He was the writer of the Gospel of Mark; the apostle Peter being the source of the Gospel.
It would appear that John Mark's father was Roman and his mother a Jewish Christian named Mary. He and his mother lived in Jerusalem.
On the apostles Paul and Barnabas' first missionary journey, John Mark accompanied them for a short time. He turned back, however, at some point.
On Barnabas' second missionary journey, he accompanied his uncle Barnabas to the island of Cyprus where Barnabas was martyred. It is, also, possible that the apostle Peter was the one who led him to Christ Jesus.
He was, also, a "great comfort" to the apostle Paul during his imprisonment in Rome (we also see him with the apostle Peter in Babylon.)
After the deaths of the apostles Peter and Paul in Rome, John Mark went to Alexandria, a Greco-Roman city in Egypt with a large Jewish population. It's believed that he was the pastor of the church at Alexandria and at some point, John Mark was martyred there.
He knew many of the giants of the Apostolic age such as the apostles Peter, Paul and Barnabas, as well as Timothy. He, also, did much to advance the spread of Christianity during his time.