Son of Seleucus IV who sent him to Rome (175 BCE) as a 12 year old hostage in exchange for his uncle, Antiochus IV. When Demetrius'  father was murdered, his uncle claimed the throne, leaving him a prisoner in Rome.  Thirteen years later (162 BCE) he escaped, captured & executed his young cousin [Antiochus V] & claimed the throne for himself. 

Demetrius wasted no time in trying to crush the Jewish rebellion. His devastating defeat of Jewish forces at the battle of Elasa (160 BCE) in which the Judean leader Judah Maccabee was killed might have heralded the end of Jewish hopes for independence had he been able to concentrate all his forces on suppressing Jewish rebels.  But in 153 BCE he was faced with an even more serious threat to his rule in the person of Alexander Balas, who claimed to be a son of Antiochus IV & won support from foreign opponents who sought to counter Demetrius' territorial ambitions [Ptolemy VI, the Roman Senate & Judah Maccabee's brother, Jonathan]. He died fighting Balas' forces.

References: Josephus, Antiquities 12.389-402,415,420; 13.23,35-48,58-61.
                   1 Macc 7:1-8; 8:29-32; 9:1-18;10:1-54.
                   Justin, Epitome 39.1-2. 
                   Appian, History of Rome: Syrian Wars 46-47.
                   Livy, History: Periochae 46.

Other resources on line:

• Demetrius I Soter - Jona Lendering outlines key events & lists primary sources [Livius: Articles in Ancient History].

• 1 Maccabees 10 - Jewish account of Jonathan's use of the rivalry between Demetrius I and Alexander Balas to establish his independence  includes quotation of royal correspondence [NRSV translation posted by Bible Study Tools].

• Demetrius I Soter - brief article in Wikipedia's growing web.

Silver tetradrachma with profile of Demetrius I on the face & the seated figure of Fortune [Tyche] holding a cornucopia on the other side.  The inscription reads simply Basileos Demetriou ["of King Demetrius"].