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

full_context: Document 1: 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.
Document 2: Æthelfrith of Mercia: Æthelfrith (fl. 880s – c. 904/915) was an ealdorman of southern Mercia, who flourished in the last two decades of the ninth century and the first decade of the tenth century. His father is unknown. He was married to Æthelgyth, daughter of Æthelwulf; Æthelwulf is unidentified, but a possible candidate is King Alfred the Great's brother-in-law, the ealdorman of the Gaini who died in 901. Æthelfrith was father to four ealdormen: Æthelstan Half-King (East Anglia), Ælfstan (Mercia), Æthelwald (Kent), and Eadric (Hampshire).
Document 3: Æthelberht, King of Wessex: Æthelberht (or Ethelbert; Old English: "Æþelberht" , meaning "magnificent noble") was the King of Kent from 858 and of Wessex from 860 until his death in 865. He was the third son of Æthelwulf of Wessex and his first wife, Osburh. In 855 he became under-king of Kent while his father, Æthelwulf, visited Rome. His brother Æthelbald was left in charge of the West Saxons. After his father's death in 858 he succeeded him as king of Kent and the other eastern parts of the kingdom. When Æthelbald died childless in 860, the kingship of the West Saxons also passed to Æthelberht.
Document 4: Wulfhere of Mercia: Wulfhere or Wulfar (died 675) was King of Mercia from 658 until 675 AD. He was the first Christian king of all of Mercia, though it is not known when or how he converted from Anglo-Saxon paganism. His accession marked the end of Oswiu of Northumbria's overlordship of southern England, and Wulfhere extended his influence over much of that region. His campaigns against the West Saxons led to Mercian control of much of the Thames valley. He conquered the Isle of Wight and the Meon valley and gave them to King Æthelwealh of the South Saxons. He also had influence in Surrey, Essex, and Kent. He married Eormenhild, the daughter of King Eorcenberht of Kent.
Document 5: 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.
Document 6: 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.
Document 7: 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.
Document 8: Edward the Elder: Edward the Elder (Old English: "Eadweard cyning "; c. 874 – 17 July 924) was King of the Anglo-Saxons from 899 until his death. He became king in 899 upon the death of his father, Alfred the Great. He captured the eastern Midlands and East Anglia from the Danes in 917 and became ruler of Mercia in 918 upon the death of Æthelflæd, his sister.
Document 9: Eadric, Ealdorman of Wessex: Eadric (fl. 942–949) was a tenth-century ealdorman of Wessex. He was the youngest of four sons of Æthelfrith, an ealdorman in Mercia, and his wife Æthelgyth. From 946 until his death in 949 Eadric was the second most senior ealdorman in England, surpassed only by his brother Æthelstan Half-King.
Document 10: Eadred: Eadred (also Edred) (923 – 23 November 955) was King of the English from 946 until his death. He was the son of Edward the Elder and his third wife Eadgifu of Kent, and a grandson of Alfred the Great. Eadred came to the throne following the assassination of his older brother, Edmund I. The chief achievement of his reign was to bring the Kingdom of Northumbria under total English control, which occurred with the defeat and expulsion of Eric Bloodaxe in 954. Eadred died at the age of 32 having never married, and was succeeded by his 15-year-old nephew, Eadwig.
Document 11: Æthelweard (son of Alfred): Æthelweard (d. 920 or 922) was the younger son of King Alfred the Great and Ealhswith.
Document 12: 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.
Document 13: 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.
Document 14: Burgred of Mercia: Burgred (also Burhred or Burghred) was an Anglo-Saxon king of Mercia from 852 to 874.
Document 15: Ælfhere, Ealdorman of Mercia: Ælfhere (died in 983) was ealdorman of Mercia. His family, along with those of Æthelstan Half-King and Æthelstan Rota, rose to greatness in the middle third of the 10th century. In the reign of Edward the Martyr, Ælfhere was a leader of the anti-monastic reaction and an ally of Edward's stepmother Queen Dowager Ælfthryth. After the killing of Edward by Ælfthryth's servants in 978, Ælfhere supported the new king, Ælfthryth's son Æthelred the Unready, and was the leading nobleman in the Kingdom of England until his death in 983.
ground_truth: Beorhtweald Ealdorman of Kent