The Orontid dynasty, also known as the Eruandids or Eruandunis, ruled the Satrapy of Armenia until 330 BC and the Kingdom of Armenia from 321 BC to 200 BC. The Orontids ruled first as client kings or satraps of the Achaemenid Empire and after the collapse of the Achaemenid Empire established an independent kingdom. Later, a branch of the Orontids ruled as kings of Sophene and Commagene. They are the first of the three royal dynasties that successively ruled the ancient Kingdom of Armenia (321 BC–428 AD). Although the overthrow of Orontes IV and the accession of Artaxias I to the throne of Armenia in the early 2nd century BC is traditionally treated as the start of a new dynasty, Artaxias probably belonged to a branch of the Orontid dynasty. His descendants ruled Armenia until the 1st century AD.

Some historians state that the Orontids were of Iranian origin, and suggest that it held dynastic familial linkages to the ruling Achaemenid dynasty. Throughout their existence, the Orontids stressed their lineage from the Achaemenids in order to strengthen their political legitimacy. Their presence in Armenia is traced back to Orontes I, Satrap of Armenia in 401 BC, or further back to his ancestor Hydarnes, in the last quarter of the 6th century BC (see below).

Other historians state the Orontids were of Armenian origin, while according to Razmik Panossian, the Orontids probably had marriage links to the rulers of Persia and other leading noble houses in Armenia, and states their Armenian ethnicity is uncertain. Soviet Armenian historian Suren Yeremian writes that the Orontids were an Armenian dynasty based in the area around Lake Van, the former center of the Kingdom of Urartu. He argues that the Orontids established their rule in the Urartian capital Tushpa in 6th century BC, as that kingdom was collapsing. They expanded to other parts of Armenia to form the first Armenian kingdom. Per Yeremian, the Orontids originally came from the vicinity of Musasir (in modern-day northern Iraq), but because of the forced relocation policies of the Urartians, they came to form an Armenian enclave in the Hurro-Urartian-populated region around Lake Van.

The name Orontes is the Hellenized form of a masculine name of Iranian origin, rendered Eruand (Երուանդ) in Old Armenian (Yervand in Modern Armenian). The name is only attested in Greek (Gr.:Ὀρόντης). Its cognates are Avestan Auruuant ('brave, hero') and Middle Persian Arwand (Modern Persian Arvand). Various Greek versions of the name appear in classical sources, such as Orontas, Aroandes and Oruandes.

Despite the Hellenistic invasion of Persia, Persian and local Armenian culture remained the strongest element within society and the elites.

The imperial administration used Aramaic, where it was used in official documents for centuries. Whereas most inscriptions used Old Persian cuneiform. Xenophon used an interpreter to speak to Armenians, while some Armenian villages were conversant in Persian.

The Greek inscriptions at Armavir indicate that the upper classes used Greek as one of their languages. Under Ervand the Last (r. ca. 210–200 B.C.), the structure of government had begun to resemble Greek institutions, and Greek was used as the language of the royal court. Ervand had surrounded himself by the Hellenized nobility and sponsored the establishment of a Greek school in Armavir, the capital of the Ervanduni kingdom.

While there is no direct evidence of the Orontids' religion prior to Antiochus I of Commagene, their Iranian background and connection to the Achaemenid dynasty make it highly plausible that they followed some form of Zoroastrianism. James R. Russell contends the Armenians likely embraced Zoroastrianism during the Achaemenid era while integrating it with regional traditions.