Diodotus Tryphon, nicknamed "The Magnificent" was a Greek king of the Seleucid Empire. Initially an official under King Alexander I Balas, he led a revolt against Alexander's successor Demetrius II Nicator in 144 BC. He rapidly gained control of most of Syria and the Levant. At first, he acted as regent and tutor for Alexander's infant son Antiochus VI Dionysus, but after the death of his charge in 142/141 BC, Diodotus declared himself king. He took the royal name Tryphon Autocrator and distanced himself from the Seleucid dynasty. For a period between 139 and 138, he was the sole ruler of the Seleucid empire. However, in 138 BC Demetrius II's brother Antiochus VII Sidetes invaded Syria and brought his rule to an end.

The Seleucid Empire was a Greek power in West Asia during the Hellenistic period. It was founded in 312 BC by the Macedonian general Seleucus I Nicator, following the division of the Macedonian Empire founded by Alexander the Great, and ruled by the Seleucid dynasty until its annexation by the Roman Republic under Pompey in 63 BC.