DEIOTARUS, a prince of Gallo-Græcia, or Galatia, who joined the Romans against Mithridates, and received as his reward portions of Armenia and Pontus, with the title of king. In the civil wars he took the side of Pompey and of his patrons, the senate, against Cæsar. His own grandson, Cæsar, accused him of an intended assassination of Cæsar, which produced the fine oration of Cicero "pro Rege Deiotaro," in which the orator defended successfully his former friend. On the death of Cæsar, Deiotarus sided with Brutus; but afterwards made his peace with Octavius Cæsar, and joined him in the war against Antony, by which policy he retained possession of his territories. After this period history is silent about Deiotarus.