Pierre d'Aubusson (1423 - June 30, 1503) was a Grand Master of the order of St. John of Jerusalem (the Knights Hospitaller) and a zealous opponent of the Ottoman Empire.
Pierre probably joined the Knights of St. John in 1444 or 1445 and then left for Rhodes.
Pierre d'Aubusson was elected "Grand Prior" of the "Langue d'Auvergne" in early 1476. In June 1476, he was elected Grand Master of the Order, having been a very close associate of a previous Grand Master, Raymond Zacosta, and responsible for the repair and modernization of the fortifications of the city of Rhodes, the other castles of the Order on the islands of the Dodecanese, and the Château Saint Pierre (formerly Halicarnasse, today Bodrum, Turkey).
Sultan Mehmed II began to threaten Europe. In May 1480 a large Ottoman fleet appeared before Rhodes, carrying an invading army of some 100,000 men under the command of Mesih Pasha (originally a Greek by the name of Michael Palaiologos who had converted to Islam after the conquest of Constantinople by the Turks).
The Knights were reinforced from France by 500 knights aud 2000 soldiers under d'Aubusson's brother Antoine. The siege lasted until August. After three unsuccessful attempts againsts the City, the Turkish force was compelled to withdraw, leaving behind them 9000 dead. The siege, in which d'Aubusson was wounded three times, enhanced his renown throughout Europe.
Sultan Mehmed was furious and would have attacked the island again but for his death in 1481. His succession was disputed between his sons Bayezid and Cem. The latter, after his defeat by Bayezid, sought refuge at Rhodes under a safe-conduct from the Grand Master and the General Convent of the Order.
Rhodes not being considered secure, Cem with his own consent was sent to Bourganeuf in France where he was kept under the guard of Guy de Blanchefort, Pierre d'Aubusson's nephew.
D'Aubusson accepted an annuity of 45,000 ducats from Sultan Bayezid, in return for which he undertook to guard Cem in such a way as to prevent him from appealing to the Christian powers to aid him against his brother.
D'Aubusson's reward was a cardinal's hat (1489) and the power to confer all benefices connected with the Order without the sanction of the papacy. In addition, the Order of St. John received the assets of the Order of the Holy Sepulchre, which was merged into the Order of St. John, and a number of Italian commandries of the Knights of St. Lazarus.