Cynewulf was the King of Wessex

Wessex

The Kingdom of Wessex or Kingdom of the West Saxons was an Anglo-Saxon kingdom of the West Saxons, in South West England, from the 6th century, until the emergence of a united English state in the 10th century, under the Wessex dynasty. It was to be an earldom after Canute the Great's conquest...

 from 757 until his death in 786.

Cynewulf became king after his predecessor, Sigeberht

Sigeberht of Wessex

Sigeberht was the King of Wessex from 756 to 757.Sigeberht succeeded his distant relative Cuthred, but was then accused of acting unjustly. He was removed from power by a council of nobles, but given control of Hampshire. There, he was accused of murder, driven out and ultimately killed...

, was deposed. He may have come to power under the influence of Æthelbald of Mercia, since he was recorded as a witness to a charter of Æthelbald shortly thereafter. It was not long before Æthelbald was assassinated, however, and Mercia

Mercia

Mercia was one of the kingdoms of the Anglo-Saxon Heptarchy. It was centred on the valley of the River Trent and its tributaries in the region now known as the English Midlands...

 fell into a brief period of disorder as rival claimants to its throne fought. Cynewulf took the opportunity to assert the independence of Wessex: about 758, he took Berkshire

Berkshire

Berkshire is a historic county in the South of England. It is also often referred to as the Royal County of Berkshire because of the presence of the royal residence of Windsor Castle in the county; this usage, which dates to the 19th century at least, was recognised by the Queen in 1957, and...

 from the Mercians. Cynewulf was also often at war with the Welsh

Wales

Wales is a country that is part of the United Kingdom and the island of Great Britain, bordered by England to its east and the Atlantic Ocean and Irish Sea to its west. It has a population of three million, and a total area of 20,779 km²...

.

In 779, Cynewulf was defeated by Offa of Mercia

Offa of Mercia

Offa was the King of Mercia 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 after defeating the other claimant Beornred. In the early years of Offa's reign it is likely...

 at the Battle of Bensington, and Offa then retook Berkshire, and perhaps also London

London

London is the capital city of :England and the :United Kingdom, the largest metropolitan area in the United Kingdom, and the largest urban zone in the European Union by most measures. Located on the River Thames, London has been a major settlement for two millennia, its history going back to its...

. Despite this defeat, there is no evidence to suggest Cynewulf subsequently became subject to Offa (as his successor, Beorhtric

Beorhtric of Wessex

Beorhtric was the King of Wessex from 786 to 802.In 786, Cynewulf, king of Wessex, was killed by the exiled noble Cyneheard, brother of the former King Sigeberht. Beorhtric's successful bid for the throne was supported by Offa, king of the Mercians against Egbert...

, did).

In 786 Cynewulf was surprised and killed, with all his Thegn

Thegn

The term thegn , from OE þegn, ðegn "servant, attendant, retainer", is commonly used to describe either an aristocratic retainer of a king or nobleman in Anglo-Saxon England, or as a class term, the majority of the aristocracy below the ranks of ealdormen and high-reeves...

s present, at Merantune (now called Marten, a hamlet in the county of Wiltshire

Wiltshire

Wiltshire is a ceremonial county in South West England. It is landlocked and borders the counties of Dorset, Somerset, Hampshire, Gloucestershire, Oxfordshire and Berkshire. It contains the unitary authority of Swindon and covers...

), by Cyneheard the Atheling

Cyneheard the Atheling

Cyneheard the Atheling was the brother of Sigeberht, briefly King of Wessex. Sigeberht was deposed in 757 with the agreement of the Witan. Cynewulf of Wessex succeeded as King....

, brother of the deposed Sigeberht. Some historians have speculated that the relation of this in the Anglo-Saxon Chronicle

Anglo-Saxon Chronicle

The Anglo-Saxon Chronicle is a collection of annals in Old English chronicling the history of the Anglo-Saxons. The original manuscript of the Chronicle was created late in the 9th century, probably in Wessex, during the reign of Alfred the Great...

 may be an application of a traditional story and not accurate in its details.

The murder of Cynewulf was also considered to have taken place at Merton

Merton (historic parish)

Merton was an ancient parish in the Brixton hundred of Surrey, England. It was bounded by Wimbledon to the north, Mitcham to the east, Morden to the south and Kingston upon Thames to the west. The 1871 Ordnance Survey map records its area as . The parish was centred around the 12th century parish...

in Surrey, but modern historians, including the Rev G. H. Godwin now asscribe it to some place of the same name near Winchester. Trevelyan believes it to have been Merton, Surrey, however. See his History of England, Longmans, 1947 p. 68

The Story of Cynewulf and Cyneheard in The Anglo-Saxon Chronicle

Entry for the year 755 AD in The Anglo-Saxon Chronicle

A.D. 755. This year Cynewulf, with the consent of the West-Saxon council, deprived Sebright, his relative, for unrighteous deeds, of his kingdom, except Hampshire; which he retained, until he slew the alderman who remained the longest with him. Then Cynewulf drove him to the forest of Andred, where he remained, until a swain stabbed him at Privett river, and revenged the alderman, Cumbra. The same Cynewulf fought many hard battles with the Britons; and, about one and thirty winters after he had the kingdom, he was desirous of expelling a prince called Cyneard, he who was the brother of Sebright. But he having understood that the king was gone, thinly attended, on a visit to a lady at Merton, rode after him, and beset him therein; surrounding the stronghold without, ere the attendants of the king were aware of him. When the king found this, he went out of doors, and defended himself with courage; till, having looked on the etheling (prince), he rushed out upon him, and wounded him severely. Then were they all fighting against the king, until they had slain him. The king's warriors were alerted by the woman's cries to the tumult and, whosoever became ready fastest, ran to where the king lay slain. The etheling (prince) immediately offered them life and riches; which none of them would accept, but continued fighting together against him, till they all lay dead, except one British hostage, and he was severely wounded. When the king's thanes that were behind heard in the morning that the king was slain, they rode to the spot, Osric his alderman, and Wiverth his thane, and the men that he had left behind previously; and they met the etheling at the town, where the king lay slain. The gates, however, were locked against them, which they attempted to force; but he promised them their own choice of money and land, if they would grant him the kingdom; reminding them, that their relatives were already with him, who would never desert him. To which they answered, that no relative could be dearer to them than their lord, and that they would never follow his murderer. Then they offered that their relatives may have safe passage. They replied, that the same request was made to their comrades that were formerly with the king; "And we are as regardless of the result," they rejoined, "as our comrades who with the king were slain." Then they continued fighting at the gates, till they penetrated it, and slew the etheling and all the men that were with him; except one, who was the godson of the alderman, and whose life was spared, though he was often wounded. This same Cynewulf reigned one and thirty winters. His body lies at Winchester, and that of the etheling at Axminster. Their proper paternal ancestry goes in a direct line to Cerdic.