Darius III was the last king of the Achaemenid Persian Empire, ruling from 336 to 330 BC. He inherited a vast but politically strained state just as Alexander the Great invaded Asia. Darius was defeated at Issus and Gaugamela, although he repeatedly attempted to regroup and negotiate. While retreating east after the final collapse of organised resistance, he was seized and killed by the satrap Bessus, allowing Alexander to present himself as his avenger and legitimate successor.
Darius plays a major role in Mary Renault’s The Persian Boy, which views Alexander’s conquest through the Persian courtier Bagoas, and he appears in Steven Pressfield’s The Virtues of War. Historical fiction has often reduced him to a coward fleeing Alexander, but modern portrayals are more likely to emphasise the impossible strategic position he inherited, the scale of the empire he had to defend and the political calculations behind withdrawal from a lost battlefield.
In non-fiction, Darius III is discussed in Arrian’s The Campaigns of Alexander, Quintus Curtius Rufus’s The History of Alexander, and Diodorus Siculus’s The Library, Books 16-20. In Arrian’s The Campaigns of Alexander, it covers the Granicus, Issus, the siege of Tyre, Gaugamela, the pursuit of Darius III, campaigns in Bactria and Sogdiana, and the Indian campaign including the Hydaspes.