In Greek mythology, Plisthenes or Pleisthenes (Ancient Greek Πλεισθένης) is an infant son of Thyestes who, with his brother Tantalus, is slaughtered by Atreus and served to their father at a banquet — the crime at which the sun itself was said to hide its face. The name also belongs to other shadowy figures in the house of Tantalus, above all a son of Atreus sometimes called the father of Agamemnon and Menelaus.
Adapted from Wikipedia, "Pleisthenes" · CC BY-SA 4.0
I.The banquet victim
According to Hyginus and related Atreid tradition, when Atreus discovered Thyestes' treachery he murdered Thyestes' infant children — Plisthenes and Tantalus — and served their cooked flesh to their father at a banquet. Seneca's Thyestes and later handbooks preserve the horror of the meal; the sun was said to have turned aside at the crime.
This atlas node records that banquet victim: a child of Thyestes destroyed in the feud that stains the house of Pelops, not the genealogical placeholder sometimes inserted between Atreus and the Atreid brothers.
II.Other Pleisthenes in the house
A separate tradition makes Pleisthenes son of Atreus (or of Pelops) the father of Agamemnon and Menelaus by Aerope or Cleolla; he dies young, and Atreus raises the boys, reconciling the Homeric "Atreid" label with Hesiodic and tragic "Pleisthenid" genealogy. Apollodorus once gives Aerope as Pleisthenes' wife and mother of the brothers, elsewhere as Atreus' wife.
Still other namesakes include a son of Menelaus and Helen mentioned in a Cypria fragment, and the boy Atreus unknowingly kills in Hyginus' Fabulae 86 plot (reared by Thyestes and sent against his own father). Aeschylus' Agamemnon speaks of the Pleisthenidae without fixing which branch is meant.
III.Homonyms
This atlas entry (plisthenes) is Thyestes' infant banquet victim (Hyginus Fabulae 88). It is not the father of Agamemnon and Menelaus, not Helen's son, and not the youth of Fabulae 86. Those other Pleisthenes remain prose or unpromoted namesakes.