Offa was King of
Mercia, a kingdom of
Anglo-Saxon England, 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. Offa defeated the other claimant,
Beornred. In the early years of Offa's reign, it is likely that he consolidated his control of Midland peoples such as the
Hwicce and the
Magonsæte. Taking advantage of instability in the
kingdom of Kent to establish himself as overlord, Offa also controlled
Sussex by 771, though his authority did not remain unchallenged in either territory. In the 780s he extended
Mercian supremacy over most of southern England, allying with
Beorhtric of Wessex, who married Offa's daughter
Eadburh, and regained complete control of the southeast. He also became the overlord of
East Anglia and had King
Æthelberht II of East Anglia beheaded in 794, perhaps for rebelling against him.