Demetrius II was a king of the ancient kingdom of Syria, ruling from around 145 to 139 BCE. He was a member of the Seleucid dynasty, which was established after the death of Alexander the Great. His reign was marked by efforts to regain control over territories lost to rival factions and to stabilize his kingdom. During his rule, Demetrius II faced challenges from both internal and external enemies, including the Parthians and local uprisings. His reign ended when he was captured by the Parthians, leading to a significant decline in the power of the Seleucid Empire.