Plutarch begins by trying to determine whether Aristides was rich or poor, evaluating the evidence for both sides. Though the information on Aristides’s early life is limited, he enters public life and enters into a famous rivalry with Themistocles. Aristides stands for traditional aristocratic values, integrity, and justice, while Themistocles stands for democratic values and innovation, and is willing to bend the law to get his way. Aristides becomes known for his incorruptibility, virtue, and justice. At Marathon, Aristides displays his good character by turning over power to Miltiades, the best Athenian general, so that he can lead the Greek force against the invading Persians.

Aristides becomes known as “the Just” in Athens because of his unimpeachable virtue, but his rival Themistocles eventually turns the people against him, and Aristides is ostracized. During the Second Persian War, however, Aristides is recalled and helps the Greeks win another victory against an invading Persian force. After the Persian fleet is defeated at Salamis, Aristides convinces Themistocles to drive the Persians out of Greece as quickly as possible instead of trying to trap them so that they can try to pick them off.

In a later infantry battle against the Persians, the Battle of Plataea, Aristides leads the Athenian forces.