Tiberius Caesar is the imperial title of Tiberius Claudius Nero, the Roman emperor who succeeded Augustus. He reigned from A.D. 14 until A.D. 37.
Luke dates the beginning of John the Baptist’s ministry to the fifteenth year of Tiberius’s reign. Jesus taught and suffered under his authority, and the Gospels refer to him also simply as Caesar.
Tiberius was the stepson of Augustus. The supplied material describes him as a ruler whose reign included both administrative ability and a reputation for cruelty and vice.