Demetrius I. (Soter) (Gr. saviour), king of Syria, born about 187 B. C, died in 150. He was the son of Seleucus Philopator, and grandson of Antiochus the Great. Sent as hostage to Rome by his father, he remained there during the whole reign of Antiochus Epiphanes, after whose death in 164 he besought the senate to release him and acknowledge him as king of Syria. This being refused, he escaped secretly from Rome, landed at Tri-polis in Phoenicia, and was hailed as king by the Syrians. The young Antiochus V. and his tutor Lysias were put to death (162); and rich presents and ready subservience procured the acknowledgment of the new reign by the Romans. Delivering Babylon from a despotic governor, he received his surname of Soter from the gratitude of that city. In his war against the revolted Jews his lieutenant Nica-nor was routed by Judas Maccabseus, who also concluded a treaty of alliance with the Romans against Demetrius. His interference in the affairs of Cappadocia still more alienated the senate of the republic, and his oppressive rule and debauchery disgusted his own people.
Instigated by the deposed governor of Babylon, one Balas rose against him, claiming to be Alexander, son of Antiochus Epiphanes, and, assisted by the Romans, Jews, and Cappadocians, finally vanquished him in battle. Demetrius was slain in his flight. Demetrius Nicator and Antiochus Sidetes, his sons, reigned successively after him.