Mithridates was a young Persian

Achaemenid Empire

The Achaemenid Empire , sometimes known as First Persian Empire and/or Persian Empire, was founded in the 6th century BCE by Cyrus the Great who overthrew the Median confederation...

 soldier in the army of king Artaxerxes II who according to a version in Plutarch

Plutarch

Plutarch then named, on his becoming a Roman citizen, Lucius Mestrius Plutarchus , c. 46 – 120 AD, was a Greek historian, biographer, essayist, and Middle Platonist known primarily for his Parallel Lives and Moralia...

's Life of Artaxerxes II, accidentally killed the rebel claimant to the throne Cyrus the Younger

Cyrus the Younger

Cyrus the Younger, son of Darius II of Persia and Parysatis, was a Persian prince and general. The time of his birth is unknown, but he died in 401 B.C. The history of Cyrus and of the retreat of the Greeks is told by Xenophon in his Anabasis. Another account, probably from Sophaenetus of...

 in the Battle of Cunaxa

Battle of Cunaxa

The Battle of Cunaxa was fought in 401 BC between Cyrus the Younger and his elder brother Arsaces, who had inherited the Persian throne as Artaxerxes II in 404 BC. The great battle of the revolt of Cyrus took place 70 km north of Babylon, at Cunaxa , on the left bank of the Euphrates River...

 (Greek

Greek language

Greek is an independent branch of the Indo-European family of languages. Native to the southern Balkans, it has the longest documented history of any Indo-European language, spanning 34 centuries of written records. Its writing system has been the Greek alphabet for the majority of its history;...

: Κούναξα).

Account of events

Shortly after, Cyrus's death was reported to the king, Artaxerxes. Mithridates was given rich presents by the king, as defeating Cyrus secured Artaxerxes position as king. However, it was Artaxerxes' wish that all men think it was he and he alone who had slain Cyrus, thus Mithridates was given the rewards for conveying the horse trappings of Cyrus to the king.
A while later when invited to a banquet, Mithridates then boasted that he was the one that killed Cyrus, not realizing that he was inducing his own undoing.

Execution

The method by which Mithridates was executed is known as scaphism

Scaphism

Scaphism, also known as the boats, was an ancient Persian method of execution designed to inflict torturous death. The name comes from the Greek word skaphe, meaning "scooped out"....

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