Cleopatra I or Cleopatra Thea, surnamed Eueteria was a ruler of the Hellenistic Seleucid Empire. She was queen consort of Syria from 150 to about 125 BC as the wife of three Syrian kings: Alexander Balas, Demetrius II Nicator, and Antiochus VII Sidetes. She ruled Syria from 125 BC after the death of Demetrius II Nicator, eventually in co-regency with her son Antiochus VIII Grypus until 121 or 120 BC.

Alexander I Theopator Euergetes, surnamed Balas, was the ruler of the Seleucid Empire from 150 BC to August 145 BC. Picked from obscurity and supported by the neighboring Roman-allied Kingdom of Pergamon, Alexander landed in Phoenicia in 152 BC and started a civil war against Seleucid King Demetrius I Soter. Backed by mercenaries and factions of the Seleucid Empire unhappy with the existing government, he defeated Demetrius and took the crown in 150 BC. He married the princess Cleopatra Thea to seal an alliance with the neighboring Ptolemaic kingdom. His reign saw the steady retreat of the Seleucid Empire's eastern border, with important eastern satrapies such as Media being lost to the nascent Parthian Empire. In 147 BC, Demetrius II Nicator, the young son of Demetrius I, began a campaign to overthrow Balas, and civil war resumed. Alexander's ally, Ptolemaic king Ptolemy VI Philometor, moved troops into Coele-Syria to support Alexander, but then switched sides and threw his support behind Demetrius II. At the Battle of the Oenoparus River in Syria, he was defeated by Ptolemy VI and he died shortly afterward.