Demetrius grew up in Rome as a hostage, but returned to Greek Syria and overthrew his young cousin Antiochus V Eupator and regent Lysias.

[2] Rome taking prominent Seleucid family members hostage was one of the terms of the Treaty of Apamea that had ended the Roman-Seleucid War.

[2] Two years later, Antiochus V was greatly weakened because Rome sent an emissary to sink his ships and hamstring his elephants using the terms of the Treaty of Apamea as cause.

There he successfully gained the support of the local aristocracy and was welcomed back on the Syrian throne around November 162 BC.

Bacchides and his forces defeated and killed the rebel leader Judas Maccabaeus at the Battle of Elasa in 160 BC, restoring Seleucid control to the province for a number of years.

Demetrius acquired his surname of Soter, Savior, from the Babylonians, where he defeated the rebellious Median satrap Timarchus.

[1] Timarchus, who had distinguished himself by defending Media against the emergent Parthians, seems to have treated Demetrius' accession as an excuse to declare himself an independent king and extend his realm into Babylonia.

Demetrius' downfall may be attributed to Heracleides, a surviving brother of the defeated rebel Timarchus, who championed the cause of Alexander Balas, a boy who claimed to be a natural son of Antiochus IV Epiphanes.

Jonathan Apphus, the brother of Judas and the new leader of the Maccabees, was able to negotiate a deal with Demetrius I that would allow him to remove some of the Seleucid forces from Judea to use against Balas.