Theodore ( brother of Heraclius ) Theodore ( , , fl . ca . 610 – 636 ) was the brother ( or half - brother ) of the Byzantine emperor Heraclius ( r . 610 – 641 ) , a " curopalates " and leading general in Heraclius ' wars against the Persians and against the Arab invasions . Life . He was the son of the general and exarch of Africa Heraclius the Elder , and is usually regarded as the brother ( although John of Nikiu suggests him to be the half - brother ) of Heraclius . Soon after Heraclius ' overthrow of the tyrant Phocas ( r . 602 – 610 ) , Theodore was appointed to the crucial post of " curopalates " , controlling the palace administration , which at the time was ranked second in importance only to the imperial office itself . In 612 , after the deposition and imprisonment of the " magister militum per Orientem " Priscus , command of his troops was assumed by Theodore and Philippicus . In late 613 , Theodore accompanied his brother in a campaign against the Persians near Antioch . Although initially successful , the Byzantines were defeated and most of Cilicia conquered by the Persians . Theodore reappears in 626 , when he was sent with part of Heraclius ' army against the forces of the Persian general Shahin . Theodore heavily defeated Shahin in northeastern Anatolia , and then reportedly sailed to Constantinople , which was being besieged by the Avars . By the time he arrived , the siege was effectively at an end , but he engaged in negotiations with the Avar khagan . After conclusion of peace with Kavadh II in 628 , Theodore was sent as his brother ' s envoy to organize the Persian withdrawal from Syria and northern Mesopotamia . According to the chroniclers , the Persian garrisons were reluctant to leave , despite his bearing letters from Kavadh . This was especially the case at Edessa in 629 / 630 , where the local Jewish community allegedly encouraged the Persians to stay ; the Byzantines had to set up siege machines and begin bombarding the city before the Persians agreed to withdraw . When Theodore ' s troops entered the city , they began attacking and killing the Jews , until Heraclius , petitioned by a Jew who managed to escape , sent an order to stop this . Theodore was left by Heraclius as his virtual viceroy in the East , and entrusted with the command of Byzantine forces and the restoration of imperial authority there . In this capacity , Theodore faced the first Muslim attacks on the Byzantine provinces . He seems to have underestimated the threat ( he reportedly referred to the Arabs as " dead dogs " ) , and was unable to counter their raids . He was probably the Byzantine commander at the Battle of Mu ' tah in 629 , the first major encounter of the Muslim Arabs and the Byzantines . In 634 , he led his forces from Mesopotamia to Syria , where he apparently suffered a heavy defeat at a battle near Gabitha ( perhaps the Battle of Ajnadayn on 30 July , although other sources indicate that he was defeated in October ) . Thereafter he retreated to Edessa or Antioch , joining Heraclius . During the Byzantine counteroffensive of 636 , he re - occupied Emesa and Damascus , which had been abandoned by the Muslims . He most likely did not participate in the final Battle of Yarmouk on 20 August 636 , contrary to the reports of Muslim sources ( which also record that he was killed there ) . Instead , his failure to counter the Muslim expeditions caused a rift in his relations with Heraclius ; and Theodore allegedly criticized his brother ' s controversial marriage to his niece Martina . In response , Heraclius recalled Theodore to Constantinople and ordered his son Heraclonas to publicly humiliate and imprison him . This humiliation caused Theodore ' s son , also named Theodore , to participate in the abortive plot of John Athalarichos to overthrow Heraclius in 637 . Of Theodore ' s other son , Gregory , nothing is known .