Gerard (c. 1040 – September 3, 1120), variously surnamed Tum, Tune, Tenque or Thom, was the founder of the Order of the Knights of St. John of Jerusalem, or the Knights Hospitaller.

He was born possibly at Amalfi, or according to other accounts Martigues in Provence, while one authority even names the Chateau d'Avesnes in Hainaut. Either as a soldier or a merchant, he found his way to Jerusalem, where a hospice had for some time existed for the convenience of those who wished to visit the Christian holy places. Of this institution Gerard became guardian or provost at a date not later than 1100, and here he organized that religious order of St John which received papal recognition from Paschal II in 1113, by the bull Geraudo institutori ac praeposito Hirosolimitani Xenodochii. It was renewed and confirmed by Calixtus II shortly before the death of Gerard in 1120.

Raymond du Puy de Provence (1083 - 1160), was a French knight and was Grand Master of the Order of St. John of Jerusalem (Knights Hospitaller) from 1118-1160. He was the son of Hughes Du Puy (1060-?), Seigneur de Pereins, d'Apifer, et de Rochefort, Governor of Acre and a general of Godfrey of Bouillon. He was also a relative of Adhemar of Le Puy, the papal legate during the First Crusade. As the second Grand Master he developed the Knights Hospitaller into strong military power. He accepted the eight- pointed Amalfi cross as an official symbol of the Order, which later became known as the Maltese Cross after the establishment of the Order on Malta. Raymond divided the Order into clerical, military, and serving brothers and established the first significant Hospitaller infirmary near the Church of the Holy Sepulchre in Jerusalem. He was present at the capture of Ascalon in 1153.

Gilbert of Assailly (d.1183) was Grand Master of the Knights Hospitallers from 1162/3 to 1170, when he resigned or was deposed. During his time at the head of the Hospitallers, they purchased the land for Castle Belvoir, at Kawkab al-Hawa, now Beit She'an, and otherwise expanded their fortifications. Gilbert also began regulating the constitution of the order. His is principally remembered for his militant attitude to the invasion of Egypt, proposed by Amalric I of Jerusalem. The 1168 expedition turned out disastrously, and Gilbert's position became untenable.

Jobert of Syria (also rendered Gilbert, Josberto, or Joubert) (d.1177) was the seventh Grand Master of the Knights Hospitaller from 1172 to his death, which is assumed from his disappearance from history to have occurred in 1177. He succeeded Cast de Murols (1170-1172), while Cast's predecessor, Gilbert d'Aissailly, who was still living, had been deposed. The memory of Gilbert must have informed Jobert how not to waste the Order's funds, for he seems to have been a responsible steward of the order's assets. He set aside property for the production of white bread for the poor at the hospital in Jerusalem.

In August 1174, he refused to commit, along with the other Orders, to aiding the Sicilian navy in attacking Egypt with Miles de Plancy, the regent of the Kingdom of Jerusalem. In December, however, he joined the new regent, Raymond III of Tripoli, in a planned attack on Sultan Saladin. He and his forces were with the army which menaced Homs after Saladin had taken it. Battle was not engaged, and the Franks left in exchange for the release of hostages and remission of ransoms.

In 1176, Baldwin IV of Jerusalem confirmed a grant of lands in Egypt to the Order in exchange for assistance from Jobert in the planned campaign there. Though Jobert supported the Egyptian policy, he is last mentioned in January 1177, and his successor, Roger de Moulins, did not agree with the plan and it was abandoned.

Roger de Moulins was Grand Master of the Knights Hospitaller from 1177 to his death in 1187, succeeding Jobert of Syria.

The Hospitallers were rivals of the Knights Templar, but Pope Alexander III persuaded Roger to make a truce with them in 1179. In 1184 he toured Europe with Arnold of Torroja, the Grand Master of the Templars, and Heraclius, the Latin Patriarch of Jerusalem, and established the Hospitaller Order in England, France and Germany. On his way back he helped the Normans attack Thessalonica in 1185.

During his time as Grand Master the Hospitallers became more involved in the politics of the Kingdom of Jerusalem. Roger opposed Raynald of Chatillon and Guy of Lusignan, and at first refused to hand over his key to the royal treasury when Guy was crowned King of Jerusalem in 1186. He took part in the raid against Saladin at Cresson near Nazareth on 1 May 1187, where he was killed by a lance-wound to the chest.

Roger was succeeded by William Borrel, who served as custodian of the Hospitallers for a brief time in 1187, and then by Armengol de Aspa, who served as provisor (custodian) until 1190. A new Grand Master was not chosen until Garnier of Nablus was elected in 1190 during the Third Crusade.

Pierre Guérin de Montaigu (d. 1230) was a nobleman from Auvergne, who became the 13th Grand Master of the Knights Hospitaller, in 1207-8.

He intervened in Armenia to help the Christian population against Suleiman of Iconium. He helped raise the siege of Acre by the Sultan of Damascus.

He distinguished himself at the capture of Damietta during the Fifth Crusade, and subsequently toured European countries seeking support. On his return to Palestine, he found turmoil; he tried vainly to reconcile the Hospitallers with the Knights Templar.

In 1228 he persuaded the Pope to break the truce holding between Christian and Muslim powers. He refused however to serve in the army commanded by Emperor Frederick II, who was excommunicated.

He died in Palestine.

Guillaume de Villaret (Occitan: Guilhem del Vilaret) (d. 1305), a native of Languedoc-Roussillon was the 24th Grand Master of the Knights Hospitallers,[1] a position he held from 1296 to his death. He was succeeded by his nephew, Foulques de Villaret, whose career he had done much to advance.

In 1300, in response to the urgent remonstrances of the knights, he appeared in Cyprus. His Order participated in an ill-fated expedition with other Cypriots, meaning the Knights Templar, the Teutonic Knights, and the Kingdom of Jerusalem, to launch coastal raids along the Egyptian, Palestine and Syrian coasts in 1300. The Cypriots, under King Henry II, then sent a land-based source to the island of Arwad, in an attempt to retake the coastal city of Tortosa. There had been some attempt to do this in concert with forces from the Mongol Ilkhanate; however the promised Mongol troops did not arrive, the Cypriots eventually had to retreat from Ruad, and the island was re-taken by the Egyptian Mamluks a year later.

Foulques de Villaret (Occitan: Folco del Vilaret, also Fulk de Villaret) (d. 1 September 1327), a native of Languedoc-Roussillon, France, was the 25th Grand Master of the Knights Hospitaller, succeeding his paternal uncle Guillaume de Villaret in 1305. His uncle had done much to foster his early career in the Order. He was appointed Admiral in 1299, and Grand Commander two years later. By 1303 he was Lieutenant of the Master, and so advanced to Master on his uncle's death.

Under his leadership they launched a successful attempt at the conquest of Rhodes, (1308 to later 1309). Other islands were also taken (Kastellórizo, Bodrum). The Order then moved its headquarters to Rhodes.

However, despite the huge benefits to his Order from the suppression of the Knights Templar (the Templars' assets were assigned to the Hospitallers by the Pope in 1312), de Villaret's campaigns of territorial expansion ran the Order heavily into debt. These debts were not paid off until the mid-1330s. De Villaret seems to have been a difficult and overbearing man, and eventually alienated his Order. Allegations were made of increasingly arrogant, even tyrannical behaviour, although none of the allegations are specific, and one Italian account of the lives of the Grand Masters claimed that he was treated unjustly.

In 1317, the Order attempted a coup against him. A group of knights went to assassinate him at his residence at Rhodini, but his chamberlain aided his escape. He fled to the Hospitaller castle at Lindos, where he was besieged by his own Order. They had, in the meantime, elected Maurice de Pagnac as Grand Master in his place, and wrote to Pope John XXII in July to justify their actions.

The Pope summoned both Grand Masters to his court at Avignon to settle the dispute. Meanwhile, Brother Giraud de Pins administered the order in the Pope's name. The Pope reappointed de Villaret – but only so that he could tender his resignation formally. Brother Hélion de Villeneuve was named as Master on 18 June 1319, the elderly de Pagnac having died in the meantime. The Pope appointed de Villaret Prior of Capua for life on 29 June, but after more problems there, he was transferred to the Priory of Rome in 1325. That, too, seems to have been unsuccessful, and after April that year, he received only a pension. He returned to his homeland, and lived as a mere Brother of the Order at his sister's home in Teyran, near Montpellier. He died on 1 September 1327, and was buried in the former Templar Church in Montpellier.

Pierre de Corneillan (died 24 August 1355) was the Grand Prior of Saint-Gilles and 4th Grand Master of the Order of St. John of Jerusalem, in Rhodes, from 1353 to 1355. His Blazon was : "Gules on a bend argent three Cornish choughs sable"

De Corneillan spent most of his brief rule (18 months) successfully resisting the intentions of Pope Innocent VI, who planned to move the seat of the Order from Rhodes, to somewhere even closer to Palestine and the Mamluk possessions. His marble sarcophagus is preserved at the main hall of the Archaeological Museum of Rhodes.

Juan Fernández de Heredia (c. 1310 – 1396) was the Grand Master of the Knights Hospitaller from 24 September 1377 to his death. His tenure was occupied by the "affair of Achaea." He was also a great patron of the translation and composition of historiographical works in the Aragonese language and a counsellor to two Kings of Aragon.

Heredia was born in Munebrega, Aragon. As a knight of the Hospitaller order (from 1328), Heredia was the commander of the castles of Villel, Aliaga, and Alfambra. He was originally patronised by Peter IV of Aragon and Pope Innocent VI. Through the aid of the latter, the priories of Castile, León, and Saint-Gilles, the richest priory of the order, were bestowed upon him. He supported Peter IV against the Union of Aragon and fought on his side in the successful Battle of Epila (1348).

In 1346, with the king of Aragon's support, he gained the castellany of Amposta (which was the priory of Aragon). Heredia made himself and his family (and illegitimate children) enormously wealthy at the expense of the order. His power and influence was greatly circumscribed by the Grand Master Raymond Berengar, but in 1371, he entered the favour of Pope Urban V and was elevated as the master's lieutenant in Western Europe.

In 1376, Heredia conducted the fleet bearing Pope Gregory XI back to Rome, presaging the end of the Avignon Papacy. The next year, on September 24, Gregory formally appointed Heredia grand master, following the death of Robert of Juilly on July 27. Heredia embarked from Naples for Romania late in 1377, arriving in Vonitsa in April 1378. Heredia immediately set about to take Arta but was captured by Ghin Boua Spata, lord of Aetolia and Arcanania, and sold to the Ottoman Turks. He was quickly ransomed, for we find him in Glarentsa on 20 May 1379, though during his absence, his commandant, Gaucher of La Bastide, hired the Navarrese Company of mercenaries and brought them to the Principality of Achaea for eight months.

After his release, Heredia went to Rhodes, the headquarters of the order, in July. Power was readily ceded to him, as he was an adherent of the Avignonese Pope Clement VII. Heredia tried to make a deal to have the Navarrese turn over the castles they were holding in the name of the prince to the military order. The Navarrese' preponderant demands, however, quickly sunk any possible agreement. Heredia ignored the powerful company and instead dealt directly with Marie of Blois, who claimed the principality on behalf of her son Louis II of Naples. Marie signed over her son's rights to the order on 24 January 1387, with the consent of Clement VII. The transaction cost the order 20,000 gold florins. Later, the pope reversed his endorsement at the request of the Achaean claimant Amadeo, Lord of Pinerolo.

Despite these failures with the Navarrese, Heredia had continued to use them in his war. Though Peter IV had forbid any Hospitallers of his realm to travel with Heredia east, he himself had claimed the rights to the Duchy of Athens. The Navarrese, under Juan de Urtubia, attacked Thebes, the capital of the duchy, and Heredia, though friendly with the king, was warned in a letter to stop abetting his enemies (10 September 1380).

Heredia spent most of his remaining life after 9 April 1382, when he embarked for the West with his powers diminished some by the untrusting convent in Rhodes, in Avignon. In April 1383, the Roman Pope Urban VI appointed Richard Caracciolo, prior of Capua, anti-master in opposition to Heredia. Caracciolo had the support of England and other Urbanist regions, but his power was insignificant by his death in 1395, after which no one was elected to replace him. Heredia did not long survive him and was succeeded by Philibert of Naillac.

Heredia was wealthy and learned, a patron of historiography and translation. It was he who ordered the Chronicle of Morea translated into Aragonese sometime before 1393, though it does not contain any mention of his term of service in the Morea.

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.