The Book of Luke is addressed to Theophilus.
The third of the Gospels is that of Luke. Luke was a companion of Saint Paul and he also wrote the Book of Acts. Both books are addressed to a man named Theophilus. We do not know who Theophilus was; the name means "lover of God" so it may be a title rather than a name. Theophilus may also have been a Roman official as he is referred to as "most excellent", a term used elsewhere to describe Roman officials.
Luke was a Greek from the city of Antioch in Syria, and he is the only Gentile author found in the New Testament. His Gospel is intended to strengthen the faith of Gentile Christians; especially Greeks. He also wants unbelieving Greeks to hear about Jesus and come to believe in Him.