Arguments are made for a few different kings deemed to control enough of the ancient kingdoms of the Anglo-Saxons to be deemed the first King of England. For example, Offa, king of Mercia, and Egbert, king of Wessex, are sometimes described as kings of England by popular writers, but not by all historians. In the late eighth century Offa achieved a dominance over southern England that did not survive his death in 796. In 829 Egbert conquered Mercia, but he soon lost control of it. By the late ninth century Wessex was the dominant Anglo-Saxon kingdom. Its king, Alfred the Great, was overlord of western Mercia and used the title King of the Angles and Saxons, but he never ruled eastern and northern England, which was then the Danelaw. His son Edward the Elder conquered the eastern Danelaw, but Edward's son Æthelstan became the first king to rule the whole of England when he conquered Northumbria in 927, and he is regarded by some modern historians as the first king of England. The title "King of the English" or Rex Anglorum in Latin, was first used to describe Æthelstan by one of his charters in 928.
The Principality of Wales was incorporated into the Kingdom of England under the Statute of Rhuddlan in 1284, and in 1301 King Edward I invested his eldest son, the future King Edward II, as Prince of Wales. Since that time, except for King Edward III, the eldest sons of all English monarchs have borne this title. After the death of Queen Elizabeth I without issue, in 1603, King James VI of Scotland also became James I of England, joining the crowns of England and Scotland in personal union. By royal proclamation, James styled himself "King of Great Britain", but no such kingdom was created until 1707, when England and Scotland united to form the new Kingdom of Great Britain during the reign of Queen Anne.
There is some evidence that Ælfweard of Wessex may have been king for up to four weeks in 924 (timing itself is unclear, as he died 16 days, not 28 days, after his father), between his father Edward the Elder and his brother Æthelstan, although he was not crowned. However, this is not accepted by all historians. Also, it is unclear whether—if Ælfweard was declared king—it was over the whole kingdom or of Wessex only: one interpretation of the ambiguous evidence is that when Edward died, Ælfweard was declared king in Wessex and Æthelstan in Mercia.
England came under the control of Sweyn Forkbeard, a Danish king, after an invasion in 1013, during which Æthelred abandoned the throne and went into exile in Normandy.