Since 57 BCE, Orodes II had been ruler of the Parthian Empire. His commander Surena had defeated the Romans near Carrhae (53 BCE), and the Romans were looking for ways to avenge themselves. In c.50 BCE, the Romans found a way: they supported a rival Arsacid ruler, prince Pacorus, who indeed attempted to revolt, but eventually made his peace with Orodes.
We learn again from Pacorus in 41, when the Romans were involved in a civil war between the adherents and the murderers of Julius Caesar, Orodes made Pacorus his co-ruler and sent him again to the west. The Parthian armies penetrated deep into Roman territory and made the Jewish high priest, the Hasmonaean Hyrcanus II, prisoner, but in the end, the Romans restored order and Pacorus was killed in action.
Pacorus was married to a sister of the Armenian king Artavasdes II.
The chronology of the Arsacid kings of the Parthian Empire is less well-understood than, for example, the sequence of Seleucid and Ptolemaic kings or the emperors of Rome. This information is based on the researches by G.R.F. Assar, as published in "Iran under the Arsakids, 247 BC – AD 224/227" in: Numismatic Art of Persia (2011).