Mithridates I, also known as Mithridates I the Great, was king of the Parthian Empire from 165 BC to 132 BC. During his reign, Parthia was transformed from a small kingdom into a major political power in the Ancient East as a result of his conquests. He first conquered Aria, Margiana and western Bactria from the Greco-Bactrians sometime in 163–155 BC, and then waged war with the Seleucid Empire, conquering Media and Atropatene in 148/7 BC. In 141 BC, he conquered Babylonia and held an official investiture ceremony in Seleucia. The kingdoms of Elymais and Characene shortly afterwards became Parthian vassals. In c. 140 BC, while Mithridates was fighting the nomadic Saka in the east, the Seleucid king Demetrius II Nicator attempted to regain the lost territories; initially successful, he was defeated and captured in 138 BC, and shortly afterwards sent to one of Mithridates I's palaces in Hyrcania. Mithridates I then punished Elymais for aiding Demetrius, and made Persis a Parthian vassal.

The Parthian Empire, also known as the Arsacid Empire, was a major Iranian political and cultural power centered in ancient Iran from 247 BC to 224 AD. Its latter name comes from its founder, Arsaces I, who led the Parni tribe in conquering the region of Parthia in Iran's northeast, then a satrapy (province) under Andragoras, who was rebelling against the Seleucid Empire. Mithridates I greatly expanded the empire by seizing Media and Mesopotamia from the Seleucids. At its height, the Parthian Empire stretched from the northern reaches of the Euphrates, in what is now central-eastern Turkey, to present-day Afghanistan and western Pakistan. The empire, located on the Silk Road trade route between the Roman Empire in the Mediterranean Basin and the Han dynasty of China, became a center of trade and commerce.