Pacorus I was a Parthian prince, who was the son and heir of Orodes II. The numismatist David Sellwood deduced that Pacorus ruled in c. 39 BC. It is uncertain whether Pacorus ruled alongside his father, or ruled independently. His wife was an unnamed Armenian princess, who was a sister of the Artaxiad king of Armenia, Artavasdes II.

Orodes II, was King of Kings of the Parthian Empire from 57 BC to 37 BC. He was a son of Phraates III, whom he murdered in 57 BC, assisted by his elder brother Mithridates IV. The two brothers quickly fell out and entered into a dynastic struggle, in which Orodes was triumphant.