Name: King Offa
Born: c.730
Parents: Thingfrith (Father)
House of: Mercia
Became King: 757
Married: Cynethryth
Children: Aelfflaed, Ecgfrith, Eadburh
Died: July 29, 796

Offa (son of Thingfrith, son of Eanulf), King of Mercia, was one of the leading figures of Saxon history. He obtained the throne of Mercia in 757, after the murder of his cousin, King Aethelbald, by Beornraed. After spending fourteen years in consolidating and ordering his territories he engaged in conquests which made him the most powerful king in England. After a successful campaign against the Hestingi, he defeated the men of Kent at Otford (776); the West Saxons at Bensington in Oxfordshire (779); and finally the Welsh, depriving the last-named of a large part of Powys, including the town of Pengwern. To repress the raids of the Welsh he built Offa’s dyke, 150 miles long and roughly indicating for the first time what has remained the boundary between England and Wales.

From 776 Offa was the most powerful Anglo-Saxon king until Alfred the Great. He ruled over Kent, Sussex, East Anglia and the Midlands, and allied with Beorhtric of Wessex. His rule never extended to Northumbria but his daughter married the King of Northumbria. Offa died in 796.

Timeline for King Offa  
 757  Offa seizes the Kingdom Mercia after the murder of his cousin Aethelbald.
 776  Defeats the men of Kent at Otford
 779  Offa defeats Cynewulf of Wessex at Bensington in Oxfordshire.
 784  Offa defeats the Welsh. Around this time work on Offa’s Dyke is started marking the border with Wales.
 785  Egbert son of Eahmund of Kent flees to Wessex and then to exile in the Frankish court of Charlemagne
 787  1st recorded Viking raids on England
 789  Beorhtric of Wessex marries Offa’s daughter Eadburgh
 792  Aethelred king of Northumbria marries Offa’s daughter Aelfflaed
 793  St Albans Abbey founded. Offa annexes East Anglia and joins it to the kingdom of Mercia
 793  Vikings raid the Christian monastery on Lindisfarne
 795  Vikings raid the monastery on Iona in Scotland
 796  Offa’s dyke is completed. The death of Offa marks the end of Mercian supremacy in England. His son Ecgfrith reigns for less than 6 months

Credit:
http://www.britroyals.com/