Onasander or Onosander (Greek: Ὀνήσανδρος Onesandros or Ὀνόσανδρος Onosandros; fl. 1st century AD) was a Greek philosopher. He was the author of a commentary on the Republic of Plato, which is lost, but we still possess his Strategikos (Στρατηγικός), a short but comprehensive work on the duties of a general. It is dedicated to Quintus Veranius, consul in AD 49, and legate of Britain. It was the chief authority for the military writings of the emperors Maurice and Leo VI, and Maurice of Saxony, who consulted it in a French translation and expressed a high opinion of it.