Question: Whose father was an Anglo-Saxon king of Mercia from 852 to 874?

Context paragraphs:
Beorhtweald Ealdorman of Kent: Beorhtweald Ealdorman of Kent was an English ruler of the 9th Century AD.  His father was Burgred of Mercia, his mother: Æthelswith, and his brother,: Beorhtnoð æthling of Kent.

Mercian Supremacy: The "Mercian Supremacy" the period of Anglo-Saxon history between 600 and 900, when the kingdom of Mercia dominated the Anglo-Saxon Heptarchy.  Sir Frank Stenton apparently coined the phrase; he argued that Offa (ruled 757–796) achieved the unification of England south of the Humber estuary under Mercia.  Scholastic opinion on the relationship between the kingdoms of Wessex and Mercia at this time remains divided.

Southumbrians: The Southumbrians or 'Suðanhymbre' were the Anglo-Saxon people occupying northern Mercia.  The term might not have been used by the Mercians, and instead possibly coined by the Deiran or Bernician people as a territorial response to their own Kingdom of Northumbria.  The "Anglo-Saxon Chronicle" refers to King Coenred as having become the King of the Southumbrians in 702, two years before he became King of all the Mercians.  The fact that Coenred was the son of Wulfhere, the Mercian King, implies that Southumbria was a sub-kingdom of Mercia.

Offa's Dyke: Offa's Dyke (Welsh: Clawdd Offa ) is a large linear earthwork that roughly follows the current border between England and Wales.  The structure is named after Offa, the Anglo-Saxon king of Mercia from AD 757 until 796, who is traditionally believed to have ordered its construction.  Although its precise original purpose is debated, it delineated the border between Anglian Mercia and the Welsh kingdom of Powys.

Cynethryth: Cynethryth ("Cyneðryð"; died after AD 798) was a Queen of Mercia and wife of King Offa of Mercia and mother of King Ecgfrith of Mercia.  Cynethryth is the only Anglo-Saxon Queen consort in whose name coinage was definitely issued.

Ælfwynn: Ælfwynn was the ruler of Mercia for a few months in 918, following her mother's death.  She was the daughter of Æthelred, ruler of English Mercia, and Æthelflæd (styled The Lady of Mercia).  Following the death of her mother on 12 June 918, Ælfwynn was for a short time ruler of Mercia.  The "Anglo-Saxon Chronicle" states that she was "deprived of all control in Mercia, and was led into Wessex three weeks before Christmas".

Ceolwulf II of Mercia: Ceolwulf II (died c. 879) was the last king of independent Mercia.  He succeeded Burgred of Mercia who was deposed by the Vikings in 874.  His reign is generally dated 874 to 879 based on a Mercian regnal list which gives him a reign of five years.  However, D. P. Kirby argues that he probably reigned into the early 880s.  By 883, he had been replaced by Æthelred, Lord of the Mercians, who became ruler of Mercia under the lordship of Alfred the Great, king of Wessex.

Beorhtwulf of Mercia: Beorhtwulf (] , meaning "bright wolf"; also spelled "Berhtwulf"; died 852) was King of Mercia, a kingdom of Anglo-Saxon England, from 839 or 840 to 852.  His ancestry is unknown, though he may have been connected to Beornwulf, who ruled Mercia in the 820s.  Almost no coins were issued by Beorhtwulf's predecessor, Wiglaf, but a Mercian coinage was restarted by Beorhtwulf early in his reign, initially with strong similarities to the coins of Æthelwulf of Wessex, and later with independent designs.  The Vikings attacked within a year or two of Beorhtwulf's accession: the province of Lindsey was raided in 841, and London, a key centre of Mercian commerce, was attacked the following year.  Another Viking assault on London in 851 "put Beorhtwulf to flight", according to the "Anglo-Saxon Chronicle"; the Vikings were subsequently defeated by Æthelwulf.  This raid may have had a significant economic impact on Mercia, as London coinage is much reduced after 851.

Burgred of Mercia: Burgred (also Burhred or Burghred) was an Anglo-Saxon king of Mercia from 852 to 874.

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.

Supporting paragraphs: Beorhtweald Ealdorman of Kent Burgred of Mercia
Answer: Beorhtweald Ealdorman of Kent