Mithridates or Mithradates I (ca. 195 BCE? - 138 BCE) is the "Great King" of Parthia from ca.

171 BCE - 138 BCE, succeeding his brother Phraates I.

His father is King Phriapatius of Parthia, who dies ca. 176 BCE).

Mithridates I makes Parthia into a major political power by expanding the empire to the east, south, and west.

During his reign the Parthians take Herat (in 167 BCE), Babylonia (in 144 BCE), Media (in 141 BCE) and Persia (in 139 BCE).