The story of Aeacus, Aegina, and the Three Judges is just one of many stories in Greek Mythology.
Here is their story, beginning with a quick overview.
Background
Aeacus was a king of an island in Greek Mythology called Aegina.
Aegina was born to her mother, the River God Asopus, and her father, Zeus.
Zeus took Aegina and lead her to an island by the name of Oenone. His goal was to save her from her parent's uncontrollable wrath. The island was eventually renamed Aegina after her.
Overview
Aegina gave birth to a son named Aeacus, who became the only other inhabitant of the island at that time.
Zeus took all the ants on the island and changed them into men, forming a race called the Myrmidons (the Greek word for ants) to inhabit the island of Aegina.
Aeacus then eventually became the ruler of the Myrmidons. Aeacus was considered a king of justice and piety and was asked to resolve conflicts around Greece between men and gods.
The inhabitants of Aegina also claimed that the cliffs surrounding the island had been built by their ruler to defend it from pirates.
Aeacus went to the Underworld after he died, and there he became one of the three judges, along with Minos and Rhadamanthus being the other two.
The Three Judges
The three judges of the Underworld consist of Aeacus, Minos, and Rhadamanthys.
They were all mortals and also all sons of Zeus. Zeus granted them the distinction of becoming a judge after death because of the strength of their decisions in their lives.
Since he came from Asia, Aeacus became the keeper of the keys of Hades and the representative of the colors of Hell. Rhadamanthys was Elysium's lord and Asia's shadow judge, as that was his place of origin.
With the final vote, Minos was the judge to call. The Afterlife, with its own powerful god Hades, played an important role in Greek mythology, the Underworld, and life after death was very important to the ancient Greeks.
During the time of the Titans, there were judges of the dead, but when the Olympians came into power under Zeus, it was very necessary to replace these judges of the Underworld.
The story goes that Hades came to Zeus, after a bit of time ruling, and said that the judges were now no longer able to recognize good from bad and were not good for making such judgments needed to decide the fates of souls of the dead, he continued that the judges were fooled by the outward appearance of each individual and not their true intent.
Nevertheless, the three judges would not agree on each soul's eternal future because it was said that Aeacus judged those who came from Europe, while Rhadamanthys judged those from Asia, and Minos would only determine if Aeacus or Rhadamanthys were uncertain.
The judges of the underworld's judgment would see the dead spend eternity in Elysium if they were worth it or Tartarus if they were evil.