Note: In the list of Sovereigns of Britain by Encyclopaedia Britannica, Aethelstan is the first listed as "Sovereigns of England", the prior ones are listed as "Kings of Wessex (West Saxons)".
Athelstan, also spelled Aethelstan or Ethelstan (d. 27 Oct 939), first West Saxon king to have effective rule over the whole of England.
On the death of his father, Edward the Elder, in 924, Athelstan was elected king of Wessex and Mercia, where he had been brought up by his aunt, Aethelflaed, Lady of the Mercians. Crowned king of the whole country at Kingston on 4 Sep 925, he proceeded to establish boundaries and rule firmly. His domination was significantly challenged in 937 when Constantine of the Scots, Owain of the Strathclyde, and Olaf Guthfrithson, claimant of the kingdom of York, joined forces and invaded England. They were routed at Brunanburh.
Six of Athelstan's extant codes of law reveal stern efforts to suppress theft and punish corruption. They are notable in containing provisions intended to comfort the destitute and mitigate the punishment of young offenders. The form and language of his many documents suggest the presence of a corps of skilled clerks and perhaps the beginning of the English civil service. [Encyclopaedia Britannica]
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Following copied from Barry Hummel, Jr, World Connect db=siderhummel, rootsweb.com:
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Edward's heir Athelstan (reigned 925-39) was also a distinguished and audacious soldier who pushed the boundaries of the kingdom to their furthest extent yet. In 927-8, Athelstan took York from the Danes; he forced the submission of king Constantine of Scotland and of the northern kings; all five Welsh kings agreed to pay a huge annual tribute (reportedly including 25,000 oxen), and Athelstan eliminated opposition in Cornwall. The battle of Brunanburh in 937, in which Athelstan led a force drawn from Britain and defeated an invasion by the king of Scotland in alliance with the Welsh and Danes from Dublin, earned him recognition by lesser kings in Britain.
Athelstan's law codes strengthened royal control over his large kingdom; currency was regulated to control silver's weight and to penalise fraudsters. Buying and selling was mostly confined to the burhs, encouraging town life; areas of settlement in the midlands and Danish towns were consolidated into shires. Overseas, Athelstan built alliances by marrying four of his half-sisters to various rulers in western Europe. He also had extensive cultural and religious contacts; as an enthusiastic and discriminating collector of works of art and religious relics, he gave away much of his collection to his followers and to churches and bishops in order to retain their support. Athelstan died at the height of his power and was buried at Malmesbury; a church charter of 934 described him as 'King of the English, elevated by the right hand of the Almighty ... to the Throne of the whole Kingdom of Britain'.
Little is known about the reigns of childless Athelstan's immediate successors. His half brother Edmund successfully suppressed rebellions by the Mercian Danes, but he was murdered at a feast in his own hall, at the age of 25 in 946, after seven years on the throne. Edmund's brother Edred (reigned 946-55) also dealt with trouble from Danes in the north; he brought up Edmund's sons as his heirs. The elder son Edwy was crowned by Oda, Archbishop of Canterbury, in 956 at Kingston-on-Thames (sited on the Wessex/Mercia border, and on the frontier between Alfred's kingdom and the Danelaw, this was where most recorded West Saxon consecrations took place). Aged 13 at his succession, Edwy became entangled in court factions, and Mercia and Northumbria broke away in rebellion. Edwy died before he was 20.