https://en.wikipedia.org/wiki/Vologases_IV

Vologases IV

Vologases IV of Parthia (Parthian: Walagash, Persian: بلاش‎‎, Balāsh) was the ruler of the Parthian Empire from 147 to 191. He was the son of Mithridates IV of Parthia (129–140).

Biography

Vologases, during his early reign, united the two halves of the empire which had been split between his father and Vologases III of Parthia (105–147). He also reconquered the kingdom of Characene which seems to have been independent since the Roman invasion of the Parthian empire under Trajan (98–117). Vologases IV may be the king Volgash of the Zoroastrian tradition, who began the gathering of the writings of Zoroaster.

Conflicts with Rome began in about 155 with a dispute, as usual, over the Kingdom of Armenia. In 162–166 the Parthians attacked the Roman Empire under Roman emperor Marcus Aurelius. Although the Roman–Parthian War started auspiciously for the Parthians, after the Romans recovered from the first shock and setbacks, they counterattacked and restored Sohaemus to the Armenian throne and invaded the Parthian empire.

In this war the city of Seleucia on the Tigris was destroyed and the palace at the capital Ctesiphon was burned to the ground by Avidius Cassius in 165. The Roman legions advanced as far as Media. Vologases IV made peace but was forced to cede western Mesopotamia to the Romans.

The end of his reign was marred by the revolt of Osroes II of Parthia (190), who appears to have set himself up in Media as a rival King in hope of succeeding Vologases IV. In the event the son of Vologases IV, Vologases V (191–208) of the Arsacid cadet branch dynasty, ruling Armenia, won the succession, and appears to have quickly put down Osroes II.

Source :

https://en.wikipedia.org/wiki/Vologases_IV