Don John of Austria (February 24, 1547 - October 1, 1578), also known as Juan De Austria and Don Juan de Austria, was the illegitimate son of Charles V, Holy Roman Emperor and a military leader whose most famous victory was at the naval Battle of Lepanto in 1571.

Born in Regensburg, Germany, the progeny of a liaison between Charles and Barbara Blomberg , a burgher's daughter, Don John was raised anonymously in Spain before being recognised by Philip II of Spain as a half-brother and given an income and his title. Philip had planned that Don John would enter the Church but was unable to stem his enthusiasm for a military career. Don John's first engagement in 1568 was against Moorish pirates and success entailed his appointment at the head of the Spanish forces ranged against the Morisco rebellions in Grenada.

In 1571, at the height of Don John's prestige, Philip set him at the head of the navy of the Holy League whom Don John, by authority and charisma, was able to unite in the defeat of the Turks at the Battle of Lepanto in 1571.

The victory fired Don John's ambitions but Philip was not enthusiastic to allow his bastard half-brother to establish too secure a niche in European politics. Philip hoped that the appointment as governor of the Spanish Netherlands in 1576 would allow some outlet for his ambitions but Don John resisted and only accepted on the understanding that he would be allowed to marry Mary I of Scotland, then held captive in England, by invading and staging a "liberation".

His entanglement in Dutch politics and the deteriorating relationship with Philip frustrated his plans and he died in Bouges , near Namur (currently in Belgium.)