Who had dreamed up the idea of ostracism? The same man who had introduced the concept of democratic government to Ancient Greece. His name was Cleisthenes (570?-507 BC) and along with the principle behind ostracism (to safeguard democracy in such a way that no single individual could dominate Athenian policy-making), he advocated the principle of each man being individually responsible as a citizen of Athens rather than as a member of a clan which had been the case till then.
Themistocles wasn't the only man to be ostracized. Each year a vote took place in the Assembly as to whether a vote for ostracizing should take place. Among the famous men who were ostracized after Themistocles were Aristides, Cimon, and Thucydides.
Aristides (530?-468? BC) was one of the men who fought in the Battle of Marathon. He was ostracized in 483 because of a feud between himself and Themistocles over naval policy. Three years later, the Persians once again threatened Greece and he was voted back by the Assembly. He led the Athenians against the Persians in 479n in the Battle of Plataea and won the conflict. He lived in Athens till his death.
Thucydides (460?-400 BC) was also ostracized, simply because he couldn't get the Athenian fleet to Amphipolis fast enough to save the city from falling into the hands of the Persians in 424 BC. He spent twenty years in exile. History knows Thucydides for his HISTORY OF THE PELOPONNESIAN WAR, which he himself had fought in. The HISTORY was the first study in objectivity.
Cimon (510?-450? BC) seems to have been a man with a turncoat history. He helped found the Delian League with Aristides, then following the revolt of the Helots in Sparta, was dismissed because the allies had lost confidence in him. He was ostracized in the democracy under Perikles. In other words, ostracism wasn't only used for making sure certain men didn't become a threat to Athenian democracy but also was used against men Athenians didn't trust.
