William of Malines

William of Malines (or Mesines), of Flanders (died 1145/6), was the second William who was Prior of the church of the Holy Sepulchre, from 1127 to 1130 and was thereafter elected Latin Patriarch of Jerusalem, which he remained until his death. He is sometimes called William I to distinguish him from William of Agen, second patriarch of that name.

William of Tyre described William of Mesines as a man of "praiseworthy habits". As Patriarch, he was an important supporter of Melisende during her regency and is described as a man capable yet pliable. He received a letter from Bernard of Clairvaux urging him to support the Knights Templar, who had received their papal privileges at the same time as William's embassy to Rome. William took the initiative in constructing a castle, the "Castrum Arnaldi" (or Chastel Arnoul) at Yalo, to guard the road between Jerusalem and Jaffa in 1132–33, along with some citizens. It was later a Templar stronghold. In 1139 Patriarch William was displeased by the actions of Archbishop Fulcher of Tyre (of Angoulême), who travelled to Rome to receive his pallium from the Pope and protest the division of his archdiocese into two ecclesiastical territories: the northern suffragans were under the authority of the Patriarch and only the southern sees remained under Fulcher's control. Perhaps fearing that Fulcher would try to remove his entire archdiocese to the Principality of Antioch (so that he might exercise control over it all as Archbishop), William took direct control over the southern sees of Tyre in Fulcher's absence, for William would not allow the archbishop of Tyre, whose archdiocese lay within the boundaries of the Kingdom of Jerusalem and his patriarchate, to become the subject of another.