Ecgberht was King of Wessex from 802 until his death in 839. His father was Ealhmund of Kent. In the 780s Ecgberht was forced into exile by Offa of Mercia and Beorhtric of Wessex, but on Beorhtric's death in 802 Ecgberht returned and took the throne.

In the first 20 years of Ecgberht's reign it is thought that he was able to maintain the independence of Wessex against the kingdom of Mercia, which at that time dominated the other southern English kingdoms. In 825 Ecgberht defeated Beornwulf of Mercia, ended Mercia's supremacy at the Battle of Ellandun, and proceeded to take control of the Mercian dependencies in southeastern England. In 829 he defeated Wiglaf of Mercia and drove him out of his kingdom, temporarily ruling Mercia directly. Later that year Ecgberht received the submission of the Northumbrian king at Dore. The Anglo-Saxon Chronicle subsequently described Ecgberht as a bretwalda or 'wide-ruler' of Anglo-Saxon lands.