Jean de Brienne

John I
Coronation of John and his first wife, Maria (from a 13th-century miniature)
Latin Emperor of Constantinople together with Baldwin II
Reign	1229–1237
Coronation	1231
Predecessor	Baldwin II
Successor	Baldwin II
King of Jerusalem together with Maria (1210–1212), and with Isabella II (1212–1225)
Reign	1210–1225
Coronation	3 October 1210
Predecessor	Maria
Successor	Isabella II and Frederick
Count of Brienne
Reign	1205/06–1221
Predecessor	Walter III
Successor	Walter IV
Born	c. 1170
Died	19–23 March 1237 (aged 66–67) Constantinople
Burial	Hagia Sophia, Constantinople (now Istanbul, Turkey)
Spouse	Maria of Jerusalem Stephanie of Armenia Berengaria of León
Issue	Isabella II of Jerusalem Marie, Empress Consort of Constantinople Alphonse, Count of Eu Louis, Viscount of Beaumont John
Dynasty	Brienne
Father	Érard II, Count of Brienne
Mother	Agnes of Montfaucon
Religion	Roman Catholic

John of Brienne (c. 1170 – 27 March 1237), also known as John I, was King of Jerusalem from 1210 to 1225 and Latin Emperor of Constantinople from 1229 to 1237. He was the youngest son of Erard II of Brienne, a wealthy nobleman in Champagne. John, originally destined for an ecclesiastical career, became a knight and owned small estates in Champagne around 1200. After the death of his brother, Walter III, he ruled the County of Brienne on behalf of his minor nephew Walter IV (who lived in southern Italy).

The barons of the Kingdom of Jerusalem proposed that John marry Maria, Queen of Jerusalem. With the consent of Philip II of France and Pope Innocent III, he left France for the Holy Land and married the queen; the royal couple were crowned in 1210. After Maria's death in 1212 John administered the kingdom as regent for their infant daughter, Isabella II; an influential lord, John of Ibelin, attempted to dethrone him. John was a leader of the Fifth Crusade. Although his claim of supreme command of the crusader army was never unanimously acknowledged, his right to rule Damietta (in Egypt) was confirmed shortly after the town fell to the crusaders in 1219. He claimed the Armenian Kingdom of Cilicia on behalf of his second wife, Stephanie of Armenia, in 1220. After Stephanie and their infant son died that year, John returned to Egypt. The Fifth Crusade ended in failure (including the recovery of Damietta by the Egyptians) in 1221.