Luke was a doctor (Colossians 4:14). Luke was Greek and was the only Gentile Christian author in the New Testament. Luke was a close friend of Paul whom he traveled together which allowed him to interview the other disciples.
Luke also wrote Acts, so the Book of Luke and the Book of Acts go together.
1:1-4 DEDICATION TO THEOPHILUS
Dr. Luke's writings were not from his own eye-witness, but from meeting with people and telling their story, such as the original apostles, disciples, and Jesus' family. Since Luke was a physician he would have been concerned with accuracy and would have been an analytical. He would have checked out things to verify they were true and this is something we are invited to do. (John 1:46; John 21:24; Act 17:11-12). This means that Luke probably interviewed Mary. Luke's stories do not include Joseph's view. Is this because Joseph was older and had died? Matthew included Joseph's view in Matthew 1:18-25. Luke wrote about the "things that have been accomplished, fulfilled," recognizing that the Old Testament foretold Jesus' life, death, and resurrection. Luke wrote the account for Theophilus so that he could know the certainty of things. Was Theophilus a doubter of the things he had been taught who was needing proof? If so, his doubt and Luke's endeavor to squelch his doubt (beyond a shadow of a doubt) was used by God to benefit more people than can ever be counted. God took Theophilus's doubt and used it for good. No one knows who Theophilus was, but the name means "friend of God." I want to read Luke to be a faithful friend of God!