Luke the physician

Luke was a 1st century physician who was also a travelling companion to Barnabas the priest, Timothy and Paul of Tarsus in their attempts to spread Christianity across the Mediterranean areas of the Roman Empire. He, along with Matthew the tax official and Mark of Jerusalem wrote an account of the life of Jesus Christ. These accounts differed somewhat, because of a phenomenon the First Doctor called "chinese whispers". Both Luke and Mark's accounts notably post-dated Matthew's, since only Matthew was an actual disciple of Christ. (PDA: Byzantium!)

Behind the scenes
Byzantium! doesn't give its readers much in the way of identification for this individual. He's never described as "Saint Luke", because, of course, the setting for this book is before the practical founding of the Catholic Church. He is therefore only given a descriptive name of "the physician Luke".