Mithridates IV Aršakuni was King (or anti-King) between 128 and 147. He was the brother of Osroes I of Parthia (109–129). During the invasion of Mesopotamia by the Roman Emperor Trajan (98–117) in 116 he and his son Sanatruces II took up the diadem but were defeated. After the death of Osroes I in 129 he assumed the throne and continued the struggle with the rival king Vologases III of Parthia (105–147), our ancestor. Mithridates died in an attack on Commagene in 140. Mithridates IV had appointed his son Sanatruces successor, but Sanatruces fell in a battle with the Romans. Another son, Vologases IV of Parthia (147–191), took the throne after the death of Vologases III in 147.

https://en.wikipedia.org/wiki/Mithridates_IV_of_Parthia

Mithridates IV of Parthia

Mithridates IV of Parthia (flourished 1st century & 2nd century) was a Prince of Iranian and Greek ancestry. He ruled as King of the Parthian Empire from 129 to 140. Mithridates IV was the youngest son born to Vonones II from a Greek concubine and was one of the brothers of Osroes I of Parthia (109-129). During the invasion of Mesopotamia by the Roman emperor Trajan (98-117) in 116, he and his son Sanatruces II of Parthia, took up the diadem but were defeated. After the death of Osroes I in 129 he assumed the throne and continued the struggle with the rival King Vologases III of Parthia (105-147). He died in an attack on Commagene in 140. Mithridates IV had appointed his son Sanatruces II as his successor, but Sanatruces II fell in a battle with the Romans. Another son, Vologases IV of Parthia (147-191), took the throne after the death of Vologases III in 147.

Source :

https://en.wikipedia.org/wiki/Mithridates_IV_of_Parthia