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 Mithridates II until his death in 88.

Part of this entry was originally from the 1911 Encyclopedia Britannica.