Polemon I is mentioned in several sources. He was the son of a man named Zeno, a leading citizen of Laodicea, a city that was traditionally pro-Roman and had been besieged by the anti-Roman king Mithridates VI of Pontus.note[Strabo, Geography 12.8.16.] In 40 BCE, when the Parthian king Pacorus I invaded the Roman Empire, Polemon was among the defenders; according to his younger contemporary Strabo, "he was thought worthy of a kingdom because of his bravery and honesty."note[Strabo, Geography 12.8.16.] And indeed, the Roman leader Mark Antony appointed him as ruler of Iconium in Lycaonia (39 BCE).note[Strabo, Geography 12.6.1.]
Another author, Appian of Alexandria, states that Polemon was ruler in a part of Cilicia.note[Appian, Civil Wars 5.75.] This may be right, because this is closer to eastern Pontus, where Polemon suppressed the rebellion of Arsaces, a brother the last king of the Mithridatic Dynasty. It seems that as a reward, Polemon was allowed to replace the last king of Pontus, Darius, in 37 CE. In any case, he is mentioned as ruler in Pontus in 31 BCE.note[Plutarch, Mark Antony 61.2.]
In 36 BCE, Mark Antony invaded Media Atropatene, and Polemon joined his benefactor. During this campaign, which was not as successful as the Romans had wanted, he was taken captive but he was ransomed.note[Plutarch, Mark Antony 38; Cassius Dio, Roman History 49.25.4.] He returned to Mark Antony with a message from the ruler of Media Atropatene, Artavasdes, who proposed an alliance. Indeed, the Romans and Medes concluded a treaty and Polemon was rewarded with Lesser Armenia, a small state between Pontus and Armenia proper, which was the next target of Roman aggression (34 BCE). Mark Antony must have appreciated a reliable man in Lesser Armenia.
Two years later civil war broke out between Mark Antony and his fellow-triumvir, Octavian. Polemon joined Mark Antony's expeditionary force to the west,note[Plutarch, Mark Antony 61.2.] and may have been present during the battle of Actium (31 BCE). The victor, Octavian, allowed Polemon to keep his territories. (There is a parallel here to king Herod of Judaea, another client of Mark Antony who was allowed to continue his rule.) However, Polemon lost Lesser Armenia. Still, in 26 BCE he was recognized by the Senate as ally and friend of the Roman state.note[Cassius Dio, Roman History 53.25.1.]
Several years later, in 14 BCE, Octavian - now called Augustus - and his friend Agrippa asked Polemon to reorganize the Bosporan Kingdom (i.e., Crimea). The story is told by Cassius Dio:
It seems that one Scribonius, who claimed to be a grandson of Mithridates [VI Eupator of Pontus] and had married Dynamis (the daughter of Pharnaces and the granddaughter of Mithridates) and had been entrusted with the regency, was holding Bosporus under his control. Agrippa, upon learning of this, sent against him Polemon, the king of that part of Pontus bordering on Cappadocia. Polemon found Scribonius no longer alive, for the people of Bosporus, learning of his advance against them, had already put him to death; but when they resisted Polemon through fear that he might be allowed to reign over them, he engaged them in battle. But although he conquered them, he was unable to reduce them to submission until Agrippa came to Sinope with the purpose of conducting a campaign against them. Then they laid down their arms and were delivered up to Polemon; and the woman Dynamis became his wife.note[Cassius Dio, Roman History 54.25.4-7.]
The conquest of the Bosporan Kingdom turned out to be Polemon's downfall, because when he tried to suppress a revolt, he was killed (8 BCE).note[Strabo, Geography 11.2.11.] In Pontus, he was succeeded by his other wife, queen Pythodoris. A son of Polemon, Zeno, became king of Armenia in 18 CE and accepted the throne name Artaxias III.