Mithradates II, son of Ariobarzanes, was a minor when he acceded the throne 255 BC. The conflict with the Gauls escalated to an invasion of Pontos after the death of his father. They later withdrew but remained a threat and continued the war against Heraclea Pontica who was an ally of the kingdom.

SHH v4147 Athena/Nike CNG Triton XIX/2052

Mithradates maintained friendly relations with Seleucus II, whose sister Laodice (Λαοδίκη) he married 245 BC and received large portions of Phrygia for a dowry. However, this appears to have been a nominal donation because Antiochos Hierax was collecting taxes from the region 238 BC.  After an earthquake hit Rhodos 227 BC, Mithradates helped with generous donations. During the later conflict between Seleucus II and his younger brother Antiochus Hierax (Αντίοχος Ιέραξ) Mithradates supported the latter intending to weaken the Syrian kingdom. With his celtic mercenaries he defeated Seleucus near Ankyra. Mithradates II maintained friendly relations with both adversaries  during  the  following  dynastic  crisis  between  Antiochus III  the

Great and Achaeus. He gave one daugter Laodike wife to Antiochus III 222 BC and another daughter Laodike wife to Achaeus. He tried to take the prosperous city of Sinope 220 BC. However, with Rhodian support the city repulsed the attack and stayed independent to the end of the 3rd c. BC)

Mithradates II was succeeded by his son Mithradates III 220-185 BC

References

Hoover Oliver D.   2012
The Handbook 0f Greek Coinage Series, Volume 7 - Coins of Northern and Central Anatolia
CNG Lancaster/London, 2012, p. 101-102

Smith William   1846
Dictionary of Greek and Roman Biography & Mythology Vol. II
Taylor & Walton, London, 1846

Wikipedia   2017
https://de.wikipedia.org/wiki/Mithridates_II._(Pontos)
 
Χριστόπουλος Γεώργιος (Διευθυντής Εκδόσεως)  1973
Ιστορία του Ελληνικού Εθνους
Τόμος Δ', Εκδοτική Αθηνών, 1973, Σελ. 400