John of Brienne (c. 1148-1237), king of Jerusalem and Latin emperor-regent of Constantinople, was a man of sixty years of age before he began to play any considerable part in history.
He was the second son of Erard II, count of Brienne, in Champagne, and of Agnes de Montfaucon, countess of Montbéliard. Destined originally for the Church, he had preferred to become a knight, and in forty years of tournaments and fights he had won himself a considerable reputation, when in 1208 envoys came from the Holy Land to ask Philip Augustus, king of France, to select one of his barons as husband to the heiress and ruler of the Kingdom of Jerusalem. Philip selected John of Brienne, and promised to support him in his new dignity. In 1210 John married the heiress Maria (daughter of Isabella and Conrad of Montferrat), assuming the title of king in right of his wife. In 1211, after some desultory operations, he concluded a six years' truce with Malik-el-Adil; in 1212 he lost his wife, who left him a daughter, Yolande (also known as Isabella); soon afterwards he married the Armenian princess Stephanie.

The coronation of John of Brienne as King of Jerusalem, with Maria of Montferrat, from a late 13C MS of the Histoire d'Outremer, painted in Acre. (Biblioteca Medicea-Laurenziana, Florence)
In the Fifth Crusade (1218-1221) he was a prominent figure. The legate Pelagius of Albano, however, claimed the command; and insisting on the advance from Damietta, in spite of John's warnings, he refused to accept the favorable terms of the sultan, as the king advised, until it was too late. After the failure of the crusade, King John came to the West to obtain help for his kingdom. In 1223 he met Pope Honorius III and the emperor Frederick II at Ferentino, where, in order that he might be connected more closely with the Holy Land, Frederick was betrothed to John's daughter Isabella, now heiress of the kingdom.
After the meeting at Ferentino, John went to France and England, finding little consolation; and thence he travelled to Santiago de Compostela, where King Alfonso IX of Leon offered him the hand of one of his daughters and the promise of his kingdom. John passed over Alfonso's eldest daughter and heiress in favor of a younger daughter, Berengaria of Castile. After a visit to Germany he returned to Rome (1225). Here he received a demand from Frederick II (who had now married Isabella) that he should abandon his title and dignity of king, which, so Frederick claimed, had passed to himself along with the heiress of the kingdom. John was now a septuagenarian "king in exile," but he was still vigorous enough to revenge himself on Frederick, by commanding the papal troops which attacked southern Italy during the emperor's absence on the Sixth Crusade (1228-1229).
In 1229 John, now eighty years of age, was invited by the barons of the Latin Empire of Constantinople to become emperor-regent, on condition that Baldwin of Courtenay should marry his second daughter and succeed him. For nine years he ruled in Constantinople, and in 1235, with a few troops, he repelled a great siege of the city by John III Ducas Vatatzes, emperor of Nicaea, and Ivan Asen II of Bulgaria.
After this last feat of arms, which has perhaps been exaggerated by the Latin chroniclers, who compare him to Hector and the Maccabees, John died in the habit of a Franciscan friar. An aged paladin, somewhat uxorious and always penniless, he was a typical knight errant, whose wanderings led him all over Europe, and planted him successively on the thrones of Jerusalem and Constantinople.
John of Brienne married three times. By his first wife, Marie of Montferrat, he had one child, Yolande, later Queen of Jerusalem. He had also one child by his second wife, Stephanie of Armenia, a son named as successor in Armenia, but died in childhood. By his third wife, Berengaria of Castile, he had 4 children.