Adrian IV or Hadrian IV, born Nicholas Breakspear (ca. 1100 - September 1, 1159) was pope from 1154 to 1159.

Adrian IV is the only Englishman who has occupied the papal chair. It is generally believed that he was born at Abbots Langley in Hertfordshire and to have received his early education at the Abbey School, St Albans (now St Albans School).

His father was Robert, a priest of the diocese of Bath, who became a monk at St Albans. Nicholas himself, however, was refused admission to the monastery, being told by the Abbot to 'wait to go on with his schooling so that he might be considered more suitable' (Abbey chronicles). In the event he did not wait and went instead to Paris and finally became a monk of the cloister of St. Rufus near Arles. He rose to be prior and in 1137 was unanimously elected abbot.

His reforming zeal as abbot led to the lodging of complaints against him at Rome; but these merely attracted to him the favourable attention of Pope Eugene III, who created him cardinal bishop of Albano.

From 1152 to 1154 Nicholas was in Scandinavia as papal legate, organizing the affairs of the new Norwegian archbishopric of Trondheim, and making arrangements which resulted in the recognition of Östra Aros (later moved to Uppsala) as seat of the Swedish metropolitan in 1164. As a compensation for territory thus withdrawn the Danish archbishop of Lund was made legate and perpetual vicar and given the title of primate of Denmark and Sweden.

On his return Nicholas was received with great honour by Pope Anastasius IV, and on the death of the latter was elected pope on December 4, 1154. He at once endeavoured to bring down Arnold of Brescia, the leader of anti-papal sentiment in Rome. Disorders ending with the murder of a cardinal led Adrian shortly before Palm Sunday 1155 to take the previously-unheard-of step of putting Rome under the interdict. The senate thereupon exiled Arnold, and the pope, with the co-operation of Frederick I Barbarossa, was instrumental in procuring his execution.

Adrian crowned the emperor at St Peter's Basilica on June 18, 1155, a ceremony which so incensed the Romans that the pope had to leave the city, not returning until November 1156.

At the diet of Besançon in October 1157, the legates presented to Barbarossa a letter from Adrian which alluded to the beneficia or "benefits" conferred upon the emperor, and the German chancellor translated this beneficia in the feudal sense of the presentation of property from a lord to a vassal. Barbarossa was infuriated by the suggestion that he was dependent on the pope, and in the storm which ensued the legates were glad to escape with their lives, and the incident at length closed with a letter from the pope, declaring that by beneficium he meant merely bonum factum or "a good deed," the coronation. The breach subsequently became wider, and Adrian was about to excommunicate the emperor when he died at Anagni on September 1, 1159.

The following is an unaltered paragraph from the Encyclopædia Britannica, 1911 edition, but the state of research on this is unknown. In view of prevailing English attitudes towards Ireland at this time, the article may not be unbiased.

A controversy exists concerning an embassy sent by Henry II of England to Adrian in 1155. According to the elaborate investigation of Thatcher, the facts seem to be as follows. Henry asked for permission to invade and subjugate Ireland, in order to gain absolute ownership of that isle. Unwilling to grant a request counter to the papal claim (based on the forged Donation of Constantine) to dominion over the islands of the sea, Adrian made Henry a conciliatory proposal, namely, that the king should become hereditary feudal possessor of Ireland while recognizing the pope as overlord. This compromise did not satisfy Henry, so the matter dropped; Henry's subsequent title to Ireland rested on conquest, not on papal concession, and was therefore absolute. The much-discussed bull Laudabiliter is, however, not genuine.