Summary of the bio from Internet Encyclopedia of Philosophy:

An Athenian, XENOPHON was in his youth a pupil of Socrates; four of Xenophon's works purport to record actual conversations of Socrates, but only the Memorabilia is well regarded today. He then embarked on a military career. Showed himself the prototype of an adventurous leader of condottieri, with no ties of country or preference of nationality, at different times serving the Greeks, Spartans, and Lacedaemonians (against Athens, which banished him). Retired to live in Sparta with his wife, Philesia, and his children, and to write. On the downfall of the Spartan supremacy, at Leuctra in 371, Xenophon was at last expelled from his quite retreat, after remaining there about twenty years. The sentence of banishment from Athens was repealed, but he never returned to Athens. He retired to Corinth and died there some time around 357.