The correct answer to this open question is the following.
Luke wrote two letters to Theophilus, a Greek nobleman whom he called "most excellent."
We are referring to Luke and his work that appears in the Bible. This nobleman, Theophilus, is mentioned in the Gospel of Luke and also in the Acts of the Apostles. The author of the Gospel never explained or revealed really who this Theophilus was, and scholars have tried to interpret the identity of this man, such as the Roman Catholic Church and the Coptic Church. Some historians have considered also that instead of being a man, Theophilus was an onorary name.