Name the King of Wessex from 839 to 858 whose father, King Egbert, defeated Beornwulf of Mercia and who himself led the Battle of Aclea between the West Saxons and the Danish Vikings?
Æthelwulf Æthelwulf (Old English for "Noble Wolf"; died 13 January 858) was King of Wessex from 839 to 858. In 825, his father, King Egbert, defeated King Beornwulf of Mercia, ending a long Mercian dominance over Anglo-Saxon England south of the Humber. Egbert sent Æthelwulf with an army to Kent, where he expelled the Mercian sub-king and was himself appointed sub-king. After 830, Egbert maintained good relations with Mercia, and this was continued by Æthelwulf when he became king in 839, the first son to succeed his father as West Saxon king since 641.
Æthelfrith Æthelfrith (died c. 616) was King of Bernicia from c. 593 until his death. Around 604 he became the first Bernician king to also rule the neighboring land of Deira, giving him an important place in the development of the later kingdom of Northumbria. He was especially notable for his successes against the Britons and his victory over the Gaels of Dál Riata. Although he was defeated and killed in battle and replaced by a dynastic rival, his line was eventually restored to power in the 630s.