Short answers, pulled from the story.
Xenophon of Athens was a Greek military leader, philosopher, and historian born around 430 BC. He led the Ten Thousand Greek mercenaries home after Cyrus the Younger's failed attempt to seize the Achaemenid throne, and he produced a body of work spanning military strategy, political philosophy, and Socratic dialogue that has survived intact for over two millennia.
The Anabasis is Xenophon's firsthand account of the expedition of Cyrus the Younger against Artaxerxes II of Persia and the subsequent march of the Ten Thousand Greek mercenaries back to Greek territory after Cyrus was killed at the Battle of Cunaxa. It covers events from 401 BC and was later used as a field guide by Alexander the Great during his own campaign into the Achaemenid Empire.
Athens banished Xenophon because he fought alongside the Spartan king Agesilaus at the Battle of Coronea in 394 BC, aligning himself with Sparta, Athens' traditional rival. He subsequently received an estate at Scillus, where he lived for twenty-three years before the Elians confiscated it following Sparta's defeat at the Battle of Leuctra in 371 BC.
Xenophon was a student of Socrates and wrote several Socratic dialogues, including the Apology, the Memorabilia, the Symposium, and the Oeconomicus. According to Diogenes Laertius, Socrates saved Xenophon's life at the Battle of Delium when Xenophon fell from his horse.
The Cyropaedia is Xenophon's account of Cyrus the Great, founder of the first Persian Empire, presented as a portrait of the ideal ruler. Scholars including David Johnson, following Leo Strauss, have argued that it contains a subtle critique of empire, monarchy, and meritocracy beneath its apparent praise, using Cyrus as a vehicle for Xenophon's own political philosophy.
Xenophon's writings on military strategy are believed to be among the first to describe flanking manoeuvres and feints in tactical detail. Military historian Theodore Ayrault Dodge credited Xenophon as the father of the systematic military retreat and named him the greatest general who preceded Alexander the Great.