This thesis is an investigation into the image of the emperor Heraclius as depicted by the ancient sources who cover his reign (610-641 A. D.). In order to establish the relevant criteria for the portrayal of an emperor it was first necessary to provide the reader with a synopsis of writings on the role of the emperor from the time of Eusebius onwards. The reign of Heraclius was then treated in roughly chronological fashion, there follow four chapters concerning the sources' description of his military exploits, his coup, and the warfare with the Avars and the Persians, including the siege of Constantinople. Here the discussion concerns the personal role of Heraclius in events and his culpability for their outcome. Heraclius' triumph in these wars led him to seek a compromise with the Monophysite Church that was defeated by opposition from the Chalcedonian Church in the recently liberated provinces. His failure to achieve any lasting settlement is then discussed as a reason for the success of the Arab invasions that followed. Heraclius' reputation as a reformer, amongst ancient and modern authors alike, is then considered with special reference to the controversy surrounding the introduction of the themes. The last chapter is a review of the interrelationship of all the sources that describe Heraclius' reign, in an attempt to define their various influences.