The answer to this question depends on how you define the word “king”. It really also depends on how you define the word “England”. After the fall of the Roman Empire, several members of the Saxon tribes and “kings” as well as Scandinavian invaders ruled England and various regions of the United Kingdom. The king who eventually became king of all England was the King of Wessex, crowned by the Archbishop of Canterbury.
The First Kings in England
King Egbert of Wessex and King Offa of Mercia are sometimes called the first kings of England. Offa ruled much of southern England in the late 8th century, but his descendants failed to keep the region as a kingdom. In 829, King Egbert of Wessex successfully conquered Mercia, but he also lost control of the region. Wessex was the largest Anglo-Saxon kingdom in the late 9th century, and Alfred the Great was crowned “King of the Anglo-Saxons”. He ruled West Mercia, but not North or East England (Danelaw).
First King of The Whole Of England
After Edward de Elder conquered eastern England (Danelaw), Athelstan had most of England under his control. He added Northumbria to his kingdom, which made him, properly, the first king of England.
First “King” of the United Kingdom of Great Britain
The first monarch that ruled Great Britain was a queen and not a king. Queen Anne was crowned as Queen of England, Ireland and Scotland in 1702 and in 1707 two of the kingdoms, England and Scotland became one state: the United Kingdom of Great Britain.
So, the question itself of who was the first King of England is rather simple. It is the answer that presents various layers and complications. Of course, the source has to always be considered as well. One historian could well define the various terms of “king” and “monarch” quite differently from another.
PIC: Saxons Arrive, Wikipedia, Historic UK, Pop Crush