A legendary king of Argos during the war of the "Seven Against Thebes". He was one of the three kings at Argos, along with Iphis and Amphiaraus, the husband of Adrastus's sister Eriphyle. During a feud between the most powerful houses in Argos, Talaus, Adrastus' father, was slain by Amphiaraus, and Adrastus being expelled from his dominions fled to Polybus, the king of Sicyon. When Polybus died without heirs, Adrastus succeeded him on the throne of Sicyon, and during his reign he is said to have instituted the Nemean Games.
He reconciled with Amphiaraus in later years, albeit reluctantly, because of her sister Eriphyle's persuasion, who became Amphiaraus' wife after.
Adrastus is most notably known as the rider of the immortal divine horse Arion, given to him by Heracles, and as the one leading the war of "Seven against Thebes" and the "War of Epigoni".
During the time of his reign in Argos, Adrastus had learned from an oracle that he must "yoke his daughters to a boar and a lion." Confused at the oracle, he did not act upon it until one night he happened to meet Tydeus of Calydon and Polynices of Thebes, both fugitives from their native countries, near the palace of Adrastus, and came to words and from words to blows. On hearing the noise, Adrastus hastened to them and separated the combatants, in whom he immediately recognised the two men that had been promised to him by an oracle as the future husbands of two of his daughters, for one bore on his shield the figure of a boar, and the other that of a lion.
After dampening both of the men's temper, Adrastus decided to take in both men in his patronage as a deference to the oracle's foretelling. Later, he gave his daughter Deipyle to Tydeus, and Argeia to Polynices, and at the same time promised to lead each of these princes back to his own country.
Adrastus now prepared for war against Thebes, although Amphiaraus foretold that all who should engage in it should perish, with the exception of Adrastus. Adrastus, however, decided to ignore Amphiaraus warning in a petty manner, as his past with Amphiaraus still left wound unhealed. He then summoned heroes from Argos to lead the campaign against Thebes. Thus arose the celebrated war of the Seven against Thebes, in which Adrastus was joined by six other heroes, Polynices, Tydeus, Amphiaraus, Capaneus, Hippomedon, and Parthenopaeus.
As Adrastus and the army approached Thebes, they sent Tydeus on ahead to try to talk Eteocles into abdicating the throne. He entered the city, defeated all the best Thebans at wresting, and killed all but one of the fifty men who were set in ambush to overwhelm him.
In the battle at Thebes, there were seven heroes on each side, and seven gates of the city. The Thebans learned from the seer Tiresias that only if Menoeceus, Creon's son, were sacrificed to Ares could they win the war. Menoeceus gladly killed himself outside the city. The Thebans drew lots to determine which gates they would defend. Eteocles wound up defending the gate which his brother, Polynices, was attacking.
The Thebans were soon forced from the battlefield into the city. One hero climbed atop the walls and proclaimed that even Zeus could not stop him. Shortly thereafter, he was struck by lightning. The tide of battle then began to turn against the Argives. Melanippus, one of the Theban heroes, dueled with Tydeus and both were mortally wounded. Athena obtained from Zeus a potion of immortality for Tydeus, but Amphiaraus, still angry at him for favoring the war, knew what was happening. He cut off Melanippus' head and gave it to Tydeus, who, in his rage, scooped out the brains and drank down the blood. Athena saw this when she arrived and dropped the potion in her disgust. Tydeus died, and Amphiaraus fled the scene. He was about to take a spear in the back when Zeus threw his thunderbolt, and the earth opened to swallow Amphiaraus together with his chariot.
Eteocles and Polynices met in combat and killed each other. The battle raged on, and true to Amphiaraus' forewarning, one by one of Adrastus' companion met death in the battlefiel. The war ended as unfortunately as Amphiaraus had predicted, as Adrastus alone was saved by the swiftness of his horse Arion.
After the battle, Creon, a king of Thebes, ordered that none of the fallen enemies were to be given funeral rites. Against his order, Antigone, the sister of Polynices and Eteocles, buried Polynices, as she was unable to let only one of his brother given proper funeral. Adrastus himself escaped to Athens to petition Theseus, the city's king, to attack Thebes and force the return of the bodies of the remaining five. Theseus initially refused, but was convinced by his mother, Aethra, who had been beseeched by the mothers of the fallen, to put the matter to a vote of the citizens. The Athenians marched on Thebes and conquered the city but inflicted no additional damage, taking only what they came for, the five bodies. They were laid upon a funeral pyre and Adrastus eulogized each.
Ten years after that, being unable to forgive himself of his failure and decisions, Adrastus decided to amend his past mistakes and persuaded the seven sons of the heroes who had fallen in the war against Thebes to make a new attack upon that city. He made the second war against the Thebians, kown as "The War of Epigoni". Thebes was taken and razed to the ground, after the greater part of its inhabitants had left the city on the advice of Tiresias, seer of Thebes.
The outcome results should have satisfied Adrastus. However, he only found further grieve from the War of Epigoni, as the only Argive hero that fell in this war was his son, Aegialeus. After having built a temple of Nemesis in the neighborhood of Thebes, he set out on his return home. But, weighed down by old age and grief at the death of his son, he died at Megara and was buried there.