Born at Wantage, Berkshire, in 849, Alfred was the fifth son of Aethelwulf, king of the West Saxons. At their father's behest and by mutual agreement, Alfred's elder brothers succeeded to the kingship in turn, rather than endanger the kingdom by passing it to under-age children at a time when the country was threatened by worsening Viking raids from Denmark.

Since the 790s, the Vikings had been using fast mobile armies, numbering thousands of men embarked in shallow-draught longships, to raid the coasts and inland waters of England for plunder.

Such raids were evolving into permanent Danish settlements; in 867, the Vikings seized York and established their own kingdom in the southern part of Northumbria. The Vikings overcame two other major Anglo-Saxon kingdoms, East Anglia and Mercia, and their kings were either tortured to death or fled.

Finally, in 870 the Danes attacked the only remaining independent Anglo-Saxon kingdom, Wessex, whose forces were commanded by King Aethelred and his younger brother Alfred. At the battle of Ashdown in 871, Alfred routed the Viking army in a fiercely fought uphill assault. However, further defeats followed for Wessex and Alfred's brother died.

As King of Wessex at the age of 21, Alfred (reigned 871-99) was a strongminded but highly strung battle veteran at the head of remaining resistance to the Vikings in southern England.

In early 878, the Danes led by King Guthrum seized Chippenham in Wiltshire in a lightning strike and used it as a secure base from which to devastate Wessex. Local people either surrendered or escaped (Hampshire people fled to the Isle of Wight), and the West Saxons were reduced to hit and run attacks seizing provisions when they could.

With only his royal bodyguard, a small army of thegns (the king's followers) and Aethelnoth earldorman of Somerset as his ally, Alfred withdrew to the Somerset tidal marshes in which he had probably hunted as a youth. (It was during this time that Alfred, in his preoccupation with the defence of his kingdom, allegedly burned some cakes which he had been asked to look after; the incident was a legend dating from early twelfth century chroniclers.)

A resourceful fighter, Alfred reassessed his strategy and adopted the Danes' tactics by building a fortified base at Athelney in the Somerset marshes and summoning a mobile army of men from Wiltshire, Somerset and part of Hampshire to pursue guerrilla warfare against the Danes. In May 878, Alfred's army defeated the Danes at the battle of Edington.

According to his contemporary biographer Bishop Asser, 'Alfred attacked the whole pagan army fighting ferociously in dense order, and by divine will eventually won the victory, made great slaughter among them, and pursued them to their fortress (Chippenham) ... After fourteen days the pagans were brought to the extreme depths of despair by hunger, cold and fear, and they sought peace'. This unexpected victory proved to be the turning point in Wessex's battle for survival.

Realising that he could not drive the Danes out of the rest of England, Alfred concluded peace with them in the treaty of Wedmore. King Guthrum was converted to Christianity with Alfred as godfather and many of the Danes returned to East Anglia where they settled as farmers. In 886, Alfred negotiated a partition treaty with the Danes, in which a frontier was demarcated along the Roman Watling Street and northern and eastern England came under the jurisdiction of the Danes - an area known as 'Danelaw'. Alfred therefore gained control of areas of West Mercia and Kent which had been beyond the boundaries of Wessex.

To consolidate alliances against the Danes, Alfred married one of his daughters, Aethelflaed, to the ealdorman of Mercia. Alfred himself had married Eahlswith, a Mercian noblewoman, and another daughter, Aelfthryth, to the Count of Flanders, a strong naval power at a time when the Vikings were settling in eastern England.

The Danish threat remained, and Alfred reorganised the Wessex defences in recognition that efficient defence and economic prosperity were interdependent. First, he organised his army (the thegns, and the existing militia known as the fyrd) on a rota basis, so he could raise a 'rapid reaction force' to deal with raiders whilst still enabling his thegns and peasants to tend their farms.

Second, Alfred started a building programme of well-defended settlements across southern England. These were fortified market places ('borough' comes from the Old English burh, meaning fortress); by deliberate royal planning, settlers received plots and in return manned the defences in times of war. (Such plots in London under Alfred's rule in the 880s shaped the streetplan which still exists today between Cheapside and the Thames.)

This obligation required careful recording in what became known as 'the Burghal Hidage', which gave details of the building and manning of Wessex and Mercian burhs according to their size, the length of their ramparts and the number of men needed to garrison them.

Centred round Alfred's royal palace in Winchester, this network of burhs with strongpoints on the main river routes was such that no part of Wessex was more than 20 miles from the refuge of one of these settlements. Together with a navy of new fast ships built on Alfred's orders, southern England now had a defence in depth against Danish raiders.

Alfred's concept of kingship extended beyond the administration of the tribal kingdom of Wessex into a broader context. A religiously devout and pragmatic man who learnt Latin in his late thirties, he recognised that the general deterioration in learning and religion caused by the Vikings' destruction of monasteries (the centres of the rudimentary education network) had serious implications for rulership. For example, the poor standards in Latin had led to a decline in the use of the charter as an instrument of royal government to disseminate the king's instructions and legislation.

In one of his prefaces, Alfred wrote 'so general was its [Latin] decay in England that there were very few on this side of the Humber who could understand their rituals in English or translate a letter from Latin into English ... so few that I cannot remember a single one south of the Thames when I came to the throne.'

To improve literacy, Alfred arranged, and took part in, the translation (by scholars from Mercia) from Latin into Anglo-Saxon of a handful of books he thought it 'most needful for men to know, and to bring it to pass ... if we have the peace, that all the youth now in England ... may be devoted to learning'.

These books covered history, philosophy and Gregory the Great's 'Pastoral Care' (a handbook for bishops), and copies of these books were sent to all the bishops of the kingdom. Alfred was patron of the Anglo-Saxon Chronicle (which was copied and supplemented up to 1154), a patriotic history of the English from the Wessex viewpoint designed to inspire its readers and celebrate Alfred and his monarchy.

Like other West Saxon kings, Alfred established a legal code; he assembled the laws of Offa and other predecessors, and of the kingdoms of Mercia and Kent, adding his own administrative regulations to form a definitive body of Anglo-Saxon law.

'I ... collected these together and ordered to be written many of them which our forefathers observed, those which I liked; and many of those which I did not like I rejected with the advice of my councillors ... For I dared not presume to set in writing at all many of my own, because it was unknown to me what would please those who should come after us ... Then I ... showed those to all my councillors, and they then said that they were all pleased to observe them' (Laws of Alfred, c.885-99).

By the 890s, Alfred's charters and coinage (which he had also reformed, extending its minting to the burhs he had founded) referred to him as 'king of the English', and Welsh kings sought alliances with him. Alfred died in 899, aged 50, and was buried in Winchester, the burial place of the West Saxon royal family.