Aymer Of Valence, or aethelmar, (d. 1260), bishop of Winchester, was a half-brother of Henry III. His mother was Isabelle of Angoulême, the second wife of King John, his father was Hugo of Lusignan, the count of La Marche, whom Isabelle married in 1220. The children of this marriage came to England in 1247 in the hope of obtaining court preferment. In 1250 the king, by putting strong pressure upon the electors, succeeded in obtaining the see of Winchester for Aymer. The appointment was in every way unsuitable. Aymer was illiterate, ignorant of the English language, and wholly secular in his mode of life. Upon his head was concentrated the whole of the popular indignation against the foreign favourites; and he seems to have deserved this unenviable distinction. At the parliament of Oxford (1258) he and his brothers repudiated the new constitution prepared by the barons. He was pursued to Winchester, besieged in Wolvesey castle, and finally compelled to surrender and leave the kingdom. He had never been consecrated; accordingly in 1259 the chapter of Winchester proceeded to a new election.

Aymer, however, gained the support of the pope; he was on his way back to England when he was overtaken by a fatal illness at Paris.

See W. Stubbs' Constitutional History, vol. ii. (1896); G. W. Prothero's Simon de Montfort (1877); W. H. Blaauw's Barons' War (1871).