king of Parthia who reigned 191–208/209.

He first appeared in 191 as a rebel against his father Vologeses III, whom he succeeded in 192. In 193 he stirred up a rebellion in the Roman client kingdoms of Osroene and Adiabene, but in 195 the Romans under Septimius Severus (Severus, Septimius) recovered the districts. After the Roman army departed, Vologeses again swept through Mesopotamia and restored his suzerainty over Adiabene. Subsequently Septimius Severus launched another campaign (197/198–202), advancing into Mesopotamia, occupying Nisibis, and plundering Ctesiphon. He failed, however, in his attempts to conquer the frontier fortress of Hatra. Little more is known of Vologeses' reign; he was succeeded by his son Vologeses VI (or V) in 209.