Demetrius III (d. 88 BC), called Eucaerus ("well-timed" possibly a misunderstanding of the derogative name Akairos, "the untimely one") and Philopator, was the son of Antiochus VIII Grypus.
By the assistance of Ptolemy X Lathyrus, king of Egypt, he recovered part of his father's Syrian dominions ca 95 BC, and held his court at Damascus, from where he tried to enlarge his dominions. To the south he defeated the Maccabean king Alexander Jannai in battle, but the hostility of the Jewish population forced him to withdraw. In attempting to dethrone his brother, Philip I Philadelphus, he was defeated by the Arabs and Parthians, was taken prisoner, and kept in confinement in Parthia by King Mithradates until his death in 88.
Demetrius, who had escaped from Ipsus with a considerable force, was a personage of importance; and, by supporting him in his quarrels with Cassander, and then Lysimachus, Seleucus was able to keep those princes employed.
The Jews, favored by former kings of Syria, were driven to desperation by the mad project of this self-willed monarch, who, not content with plundering the Temple to satisfy his necessities, profaned it by setting up in the Holy of Holies the image of Jupiter Olympius.
It was an advantage to Syria when Demetrius, the adult son of Seleucus Philopator, escaped from Rome, where he had been long detained as a hostage, and, putting Lysias and Eupator to death, himself mounted the throne.
Demetrius, who was a hostage at Rome, and who had heard of the death of his brother, went to the senate, and said that "he had come to Rome as a hostage while his brother was alive, but that now he was dead, he did not know 241 for whom he was a hostage.
DEMETRIUS, having possessed himself of the throne of Syria, and thinking that peace might be dangerous in the unsettled state of his affairs, resolved to enlarge the borders 242 of his kingdom, and increase his power, by making war upon his neighbours.
At the commencement of the war, Demetrius had entrusted two of his sons to a friend of his at Cnidus, with a 243 large quantity of treasure, that they might be removed from the perils of the war, and might be preserved, if fortune should so order it, to avenge their father's death.