Arsaces I of Parthia

Arsaces
King of the Arsacid dynasty
Coin of Arsaces I. The reverse shows a seated archer carrying a bow. A Greek inscription on the right reads ΑΡΣΑΚ[ΟΥ] (from the outside). The inscription below the bow is in Aramaic.
Reign	ca. 250 BC to either 246 BC or 211 BC
Successor	Arsaces II
Died	246 BC or 211 BC
Dynasty	Arsacid dynasty

Arsaces I (/ˈɑːrsəsiːz/; Persian: ارشک ٫ اشک یکم‎‎ Arshak, Greek: Ἀρσάκης) was the founder of the Arsacid dynasty of Parthia, and after whom all 30+ monarchs of the Arsacid empire officially named themselves. A celebrated descent from antiquity (the Bagratid "line") begins with Arsaces. Arsaces or Ashk has also given name to the city of Ashkabad.

The dates of Arsaces' birth and death are unknown, as is his real name. Most scholars now believe that Arsaces was a chief of the Parni, a Dahae tribe who conquered Parthia shortly before Diodotus’ revolt. It should be noted, however, that there is no agreement among classical sources regarding his origins, and doubt about the accuracy of classical and traditional sources on the matter. Moreover, even the most respected and/or frequently cited sources regarding Arsaces are later reiterations of classical sources, such as Arrian (i., preserved in Photius and Syncellus) and Strabo (xi.)

Rival theories about the origins of Arsaces and/or the Parni Dahae include:

In contrast, the circumstances of Arsaces' ascent to power are relatively well known. Around 250 BC, Andragoras, the governor of the Seleucid province of Parthia, proclaimed his independence from the Seleucid monarchs, and made his governorate an independent kingdom. At about the same time, Arsaces was elected leader of the Parni, an eastern Iranian tribe. With the Parni, Arsaces seized Astauene (or Astabene), i.e., northern Parthia. Andragoras was killed during his attempts to recover it, which left the Parni in control over the rest of Parthia as well. A recovery expedition by the Seleucids under Seleucus II did not succeed, and Arsaces and the Parni succeeded in holding Parthia proper during Arsaces' lifetime. (Arsaces II lost it in 209 BC to Antiochus III, to whom the Arsacids became vassals for the next 25 years).