Egbert was King of Wessex

Wessex

The Kingdom of Wessex or Kingdom of the West Saxons was an Anglo-Saxon kingdom of the West Saxons, in South West England, from the 6th century, until the emergence of a united English state in the 10th century, under the Wessex dynasty. It was to be an earldom after Canute the Great's conquest...

 from 802 until his death in 839. His father was Ealhmund of Kent

Ealhmund of Kent

Ealhmund was King of Kent in 784.The only contemporary evidence of him is an abstract of a charter dated in that year, in which Ealhmund granted land to the Abbot of Reculver...

. In the 780s Egbert was forced into exile by Offa of Mercia

Offa of Mercia

Offa was the King of Mercia from 757 until his death in July 796. The son of Thingfrith and a descendant of Eowa, Offa came to the throne after a period of civil war following the assassination of Æthelbald after defeating the other claimant Beornred. In the early years of Offa's reign it is likely...

 and Beorhtric of Wessex

Beorhtric of Wessex

Beorhtric was the King of Wessex from 786 to 802.In 786, Cynewulf, king of Wessex, was killed by the exiled noble Cyneheard, brother of the former King Sigeberht. Beorhtric's successful bid for the throne was supported by Offa, king of the Mercians against Egbert...

, but on Beorhtric's death in 802 Egbert returned and took the throne.

Little is known of the first 20 years of Egbert's reign, but it is thought that he was able to maintain Wessex's independence against the kingdom of Mercia

Mercia

Mercia was one of the kingdoms of the Anglo-Saxon Heptarchy. It was centred on the valley of the River Trent and its tributaries in the region now known as the English Midlands...

, which at that time dominated the other southern English kingdoms. In 825 Egbert defeated Beornwulf of Mercia

Beornwulf of Mercia

Beornwulf was King of Mercia from 823 to 825. His short reign saw the collapse of the Mercia's supremacy over the kingdoms of the Anglo-Saxon Heptarchy....

 and ended Mercia's supremacy

Mercian Supremacy

The Mercian Supremacy is a term commonly used to describe that period of English history between AD 600 and 900, in which the Kingdom of Mercia dominated the Anglo-Saxon Heptarchy...

 at the Battle of Ellandun, and proceeded to take control of the Mercian dependencies in southeastern England.