John of Austria (24 February[1] 1547 – 1 October 1578), in English traditionally known as Don John of Austria, in Spanish as Don Juan de Austria[2] and in German as Ritter Johann von Österreich, was an illegitimate son of Holy Roman Emperor Charles V. He became a military leader in the service of his half-brother, Philip of Spain and is best known for his naval victory at the Battle of Lepanto in 1571 against the Ottoman Empire.