Arsaces V or Phraates I.
PHRAATES I., subdued the Mardi, and, though he had many sons, left the kingdom to his brother Mithridates. (Just. 41.5
The reverse of the annexed coin has the inscription ΒΑΣΙΛΕΩΣ ΒΑΣΙΛΕΩΝ ΜΕΓΑΛΟΥ ΑΡΣΑΚΟΥ ΕΠΙΦΑΝΟΥΣ
Eckhel, with more probability, assigns this coin to Arsaces VI., who may have taken the title of "king of kings," on account of his numerous victories.