Question: Cuthred or Cuþræd was the King of Wessex from 740 (739 according to Simeon of Durham, 741 according to John of Worcester) until 756, He succeeded which relative and possibly his brother, King of Wessex from 726 to 740?
Context: Maysara al-Matghari (Berber: "Maysara Amteghri" or "Maysara Amdeghri", sometimes rendered "Maisara" or "Meicera"; in older Arab sources, bitterly called: "al-Ḥaqir" ('the ignoble'); died in September/October 740) was a Berber rebel leader and original architect of the Great Berber Revolt that erupted in 739-743 against the Umayyad Muslim empire.  However, he was deposed by the rebels, replaced with another Berber leader, and died or possibly was executed by them in 740.  The Berber Revolt succeeded 3 years after his death in defeating the Umayyad armies. Saint Margaret of Scotland (c. 1045 – 16 November 1093), also known as Margaret of Wessex, was an English princess of the House of Wessex.  Margaret was sometimes called "The Pearl of Scotland".  Born in exile in the Kingdom of Hungary, she was the sister of Edgar Ætheling, the shortly reigned and uncrowned Anglo-Saxon King of England.  Margaret and her family returned to the Kingdom of England in 1057, but fled to the Kingdom of Scotland following the Norman conquest of England in 1066.  In 1070 Margaret married King Malcolm III of Scotland, becoming Queen of Scots.  She was a very pious Roman Catholic, and among many charitable works she established a ferry across the Firth of Forth in Scotland for pilgrims travelling to St Andrews in Fife, which gave the towns of South Queensferry and North Queensferry their names.  Margaret was the mother of three kings of Scotland, or four, if Edmund of Scotland, who ruled with his uncle, Donald III, is counted, and of a queen consort of England.  According to the "Vita S. Margaritae (Scotorum) Reginae" ("Life of St. Margaret, Queen (of the Scots)"), attributed to Turgot of Durham, she died at Edinburgh Castle in Edinburgh, Scotland in 1093, merely days after receiving the news of her husband's death in battle.  In 1250 Pope Innocent IV canonized her, and her remains were reinterred in a shrine in Dunfermline Abbey in Fife, Scotland.  Her relics were dispersed after the Scottish Reformation and subsequently lost.  Mary, Queen of Scots at one time owned her head, which was subsequently preserved by Jesuits in the Scottish College, Douai, France, from where it was subsequently lost during the French Revolution. Æthelred I (Old English: Æþelræd, sometimes rendered as Ethelred, "noble counsel"; c. 847 – 871) was King of Wessex from 865 to 871.  He was the fourth son of King Æthelwulf of Wessex.  He succeeded his brother, Æthelberht (Ethelbert), as King of Wessex and Kent in 865. Dadhburzmihr or Dadmihr was the independent ruler (ispahbadh) of Tabaristan.  He succeeded his father Farrukhan the Great in 728 and reigned until his death in 740/741.  His 6 year old son, Khurshid succeeded him. Æthelheard (meaning roughly "Noble Stern"), also spelled Ethelheard or Æþelheard, was King of Wessex from 726 to 740.  There is an unreliable record of Æthelheard having been the brother-in-law of his predecessor, Ine, but his ancestry is unknown, perhaps making him the first King of Wessex not to be descended from Cynric by blood. Marcello Tegalliano (Latin: "Marcellus Tegalianus"; died 726) was, according to tradition, the second Doge of Venice (717–726).  He is described as having hailed from Eraclea, and during his nine-year reign was apparently in great disagreement with the nearby Longobards.  He died in 726 and was succeeded by Orso Ipato. Ine was King of Wessex from 688 to 726.  He was unable to retain the territorial gains of his predecessor, Cædwalla, who had brought much of southern England under his control and expanded West Saxon territory substantially.  By the end of Ine's reign, the kingdoms of Kent, Sussex, and Essex were no longer under West Saxon domination; however, Ine maintained control of what is now Hampshire, and consolidated and extended Wessex's territory in the western peninsula. Cuthred (Old English: "Cuþræd") was the King of Kent from 798 to 807. Hilderic was the Lombard Duke of Spoleto briefly from 739 to 740.  He was the first appointee of Liutprand, King of the Lombards, against the rebellious Thrasimund II. Cuthred or Cuþræd was the King of Wessex from 740 (739 according to Simeon of Durham, 741 according to John of Worcester) until 756.  He succeeded Æthelheard, his relative and possibly his brother.
Answer: Æthelheard