Demetrius III (d. 88 BC), called Eucaerus ("well-timed" possibly a misunderstanding of the derogative name Akairos, "the untimely one") and Philopator, was a ruler of the Seleucid kingdom, the son of Antiochus VIII Grypus.
By the assistance of Ptolemy IX Lathyros, 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 Jannaeus in battle, but the hostility of the Jewish population forced him to withdraw. While attempting to dethrone his brother, Philip I Philadelphus, he was defeated by the Arabs and the Parthian Empire, and taken prisoner. He was kept in confinement in Parthia by Mithridates II until his death in 88.
This article incorporates text from a publication now in the public domain: Chisholm, Hugh, ed (1911). Encyclopædia Britannica (Eleventh ed.). Cambridge University Press.