Thrasybulus (d. 388 BC) was an Athenian general, and one of the key leaders of the democracy against the oligarchy during and after the Peloponnesian War. The first of these was the rule of the Four Hundred, established in 411 BC while the fleet was at Samos. The navy employed mostly poorer citizens and included many of the most ardent supporters of the democracy, and under Thrasybulus and Thrasyllus these declared their opposition to the revolutionaries, believing themselves to be in as good a position as the men of the city. They also recalled the exile Alcibiades, hoping by his influence to obtain an alliance with Persia.
During this time the Peloponnesian ships, under Mindarus, sailed for the Hellespont, and were intercepted by the Athenians. The Athenians weakened their center in an attempt to outflank their enemies, and initially were defeated there, but the right wing under Thrasybulus took advantage of their disorder and put them to flight (see Battle of Cynossema). The fleet had to disperse for the winter, but next spring surprised Mindarus while he was besieging Cyzicus, killing him and taking some 60 triremes. This annihilated the Peloponnesian navy, and the democrats at Athens took the opportunity to restore the old democracy.
With the final defeat of Athens at Aegospotami, in 404 BC, the Spartans set up a new oligarchy, called the Thirty Tyrants and led most notably by Critias. These executed a great number of men, while others were exiled, taking up refuge in neighboring countries who had grown dissatisfied with Sparta's leadership. Then in December, Thrasybulus and Anytus left Thebes and seized the border fort of Phyle. The first attempt to dislodge them was halted by a storm, and the second, in May, by a surprise attack. Then Thrasybulus seized the Piraeus, and managed to defeat the oligarchs in a battle on the hill of Munychia, where Critias was killed.
The Thirty were replaced by Ten, chosen to represent those genuinely interested in oligarchy as opposed to simply gaining power for themselves, but these failed to come to terms with Thrasybulus and called in the Spartans to settle matters. By then Lysander, who had set up the original oligarchy, had lost influence there, and the negotiations were carried out by Pausanias, a personal enemy of his and so inclined to be more generous to the democrats. In the end, the democracy was restored again, the oligarchs being allowed to retreat to Eleusis.
A decade later new war had broken out with the Spartans, who had made an attempt to claim their own maritime empire, but were seriously checked by the Persians at Cnidus. In 389 BC, Thrasybulus was sent out with 40 ships, ultimately to help Rhodes maintain her independence but first to levy money from her allies and to plunder when they could not receive it. They won over Thasos, Samothrace, Byzantium and Chalcedon, reestablishing Athenian supremacy in the Propontis, and expelled the Spartans from Lesbos. At Aspendus, however, the locals were outraged by the violent Greek soldiers, and at night surprised and killed Thrasybulus in his tent.
Thrasybulus was also the tyrant of Miletus in the 7th century BC. He was an ally of Periander, the tyrant of Corinth.