Adhemar (also known as Adémar, Aimar, or Aelarz) de Monteil (died 1 August 1098) was one of the principal figures of the First Crusade and was bishop of Puy-en-Velay from before 1087.

Among his supporters were the future Pope Urban II and Raymond of Saint-Gilles, Count of Toulouse and the richest, most powerful nobleman in France.

[citation needed] During the leg of the trip from Durazzo to Constantinople, in the Valley of Pelagonia, Adhemar was set upon by a group of Pecheneg mercenaries, when he had wandered too far from the majority of the Crusader forces.

[2] Once the army had reached Thessalonica, Adhemar decided to stay there for some time, due to sickness, whilst the Crusader forces moved onward.

[2] Adhemar negotiated with Alexius I Comnenus at Constantinople, reestablished some discipline among the crusaders at Nicaea, fought a crucial role at the Battle of Dorylaeum and was largely responsible for sustaining morale during the siege of Antioch through various religious rites including fasting and special observances of holy days.

One such time he did this, was after an earthquake during the siege of Antioch, he had the Crusaders fast for three days and had the priests and clergy perform mass and prayers.

He was extremely skeptical of Peter Bartholomew's discovery in Antioch of the Holy Lance, especially because he knew such a relic already existed in Constantinople; however, he was willing to let the Crusader army believe it was real if it raised their morale.

[2] When Kerbogha was defeated, Adhemar organized a council in an attempt to settle the leadership disputes, but died on 1 August 1098,[3] probably of typhus.