Pleistarchus is one of the characters in the film 300.
He is a prince of Sparta, the 10 year old son of King Leonidas I and his niece Gorgo, Queen of Sparta. Leonidas is shown to aggressively train his young son in sword combat in preparation for Spartan manhood. In the original draft for script of the movie, Pleistarchus has a slightly larger role than in the finished movie. A prophecy says that Pleistarchus will father a child during his 10th year. Following the death of Leonidas in battle against the army of Xerxes I of Persia, Gorgo learns from servants that her son is able to ejaculate, despite his young age. Pleistarchus arrogantly tells his mother that he will "fill a dozen Spartan women's bellies with his seed" and surpass his father in ruling Sparta. Gorgo refutes her son and has herself declared the acting ruler of Sparta.
The role of Pleistarchus was portrayed by Giovani Cimmino.
He doesn't appear in 300: Rise of an Empire, because of Cimmino's retirement from acting.