Æthelstan or Athelstan (Old English: Æþelstan, Æðelstān; c. 893/895 – 27 October 939) was the King of England from 924 or 925 to 939. He was the son of King Edward the Elder and his first wife, Ecgwynn. Æthelstan's success in securing the submission of Constantine II, King of Scots, at the Treaty of Eamont Bridge in 927 allowed him to claim the title of 'king of the English', and even "by wishful extension" 'king of Britain'. Victory over Scottish and Viking forces at the Battle of Brunanburh in 937 confirmed his prestige. His reign has been overlooked, overshadowed by the achievements of his grandfather, Alfred the Great, but he is now regarded as one of the greatest kings of the West Saxon dynasty. Æthelstan was the first king of a unified England from 927, and his reign was of fundamental importance to political developments in the 10th century.

The materials for a life of Æthelstan are very limited, and the first biography, by Sarah Foot, was only published in 2011. The Anglo-Saxon Chronicle in this period is principally devoted to military events, and as Æthelstan's achievements were mainly in the reconstruction of the church and government, it is largely silent during his reign apart from recounting his military triumphs. The main source for his life is the twelfth century chronicle of William of Malmesbury, but historians are cautious about accepting his testimony, much of which cannot be verified from other sources. David Dumville goes so far as to dismiss William's account entirely, regarding him as a "treacherous witness" whose account is unfortunately influential. However, Sarah Foot is inclined to accept Michael Wood's argument that William's chronicle draws on a lost life of Æthelstan, while cautioning that we have no means of discovering how far William 'improved' on the original.