Darius: king of Pontus (r.39-37 BCE).
The kingdom of Pontus, once a powerful state in Anatolia, had come to an end: its king Mithridates VI Eupator had waged endless wars, but had been defeated by the Roman commanders Lucullus and Pompey (63 BCE). Mithridates' son Pharnaces II had tried to restore the old kingdom, but had been defeated by Julius Caesar in the battle of Zela (47 BCE), and had been killed by his deputy Asander.
Caesar gave Pontus to a man named Mithridates of Pergamon but at least the western part of Pontus became a Roman province.note[Appian, Mithridatic War 120.] Not much later, Caesar was assassinated and there was a civil war between his followers and his assassins. Eventually, it was Caesar's right-hand man Mark Antony who reorganized the eastern provinces. An account is given by Appian of Alexandria:
He set up kings here and there as he pleased, on condition of their paying a prescribed tribute: in Pontus, Darius, the son of Pharnaces and grandson of Mithridates: in Idumea and Samaria, Herod: in Pisidia, Amyntas; in a part of Cilicia, Polemon, and others in other countries.note[Appian, Civil Wars 5.75.]
So, Darius, a son of Pharnaces and his Sarmatian queen, was recognized as king in those parts of Pontus that were not governed by the Romans or Mithridates of Pergamon.
He was not the only son, however. According to Strabo, Darius' brother Arsaces tried to establish a state for himself, but was forced to retreat to the mountains behind the old capital of Pontus, Amasia. His refuge was a mountain fort called Sagylium.
Here Arsaces ... who was playing the dynast and attempting a revolution without permission from any of the prefects, was captured and slain. He was captured, however, not by force, although the stronghold was taken by Polemon and Lycomedes, both of them kings, but by starvation, for he fled up into the mountain without provisions, being shut out from the plains, and he also found the wells of the reservoir choked up by huge rocks; for this had been done by order of Pompey, who ordered that the garrisons be pulled down.note[Strabo, Geography 12.3.38.]
Because Strabo was born in Amasia in about this age, we may assume that he had access to reliable information. Apparently, king Darius had been unable to prevent Arsaces' attempt "to play the dynast", which suggests that he either appreciated it or had not been able to govern at all.
It seems that the Romans gave Polemon, who already was in control of Cilicia, Pontus to rule as well. In any case, the Mithridatic Dynasty of Pontus had come to an end