Who is Britain's greatest monarch?

This year marks the platinum jubilee of Elizabeth II, Britain's longest-serving monarch. But which of the kings and queens since 1066 made the biggest mark on history? We asked 12 experts to offer their nominations - and to explain what made each one truly great

- Richard Oram

The king who founded modern Scotland

David I (reigned 1124–53) wielded military might and religious reform to forge some of the nation's most enduring institutions

David I was medieval Scotland's greatest ruler, and is a towering figure in British history. During a reign lasting 29 years, he redrew the political map of these islands and laid the foundations both of the Scottish state that endured for four centuries and of the institutions that still frame Scottish society today.

Youngest of the six sons of Malcolm III and St Margaret, David had never been expected to rule. Raised in England at the court of the future Henry I, he trained as a knight and judicial agent of the crown. His reward was a marriage that brought the honour of Huntingdon and claims to Northumbria.

Huntingdon gave him lordship over laymen and clerics whose military skills, literacy and administrative experience he brought north when he became king of Scots (following the early deaths of five of his elder brothers) to form a new, English-influenced government. Many of them settled there to found some of medieval Scotland's greatest families, including the Bruces and the Stewarts.

Though remembered as a saintly man who advanced the religious reform programme begun by his parents and brothers, during his early reign he used warfare to crush challenges to his power. By the 1130s he had mastered mainland Scotland, controlling a larger realm than his predecessors.