IT HAS never seemed quite fair that Mary I was singled out to acquire the epithet “Bloody” when other Tudor monarchs happily burned those with whom they had a religious disagreement and chopped the heads off anyone who threatened their grip on power. But seeing her portrait has given me pause for thought.

The 1554 portrayal of Mary is part of an exhibition, “The Tudors: Passion, Power and Politics” now at the Walker Art Gallery in Liverpool (Arts, 22 April), which gives new clues to why the Tudors exercise such a grip on the English popular imagination.

The tumultuous years from 1485 to 1603 marked an epochal shift, breaking with over a millennium of Catholicism, establishing the Church of England, and opening an era of exploration and imperial expansion. But they were also the age in which portraiture, once the exclusive province of the monarch, moved out to include courtiers, bureaucrats, and the gentry. This is the first generation of which we also have images of the power-brokers, privateers, and poets.

So we don’t just see Henry VII, with his mean little abacus fingers and beady calculating accountant eyes. We see Thomas More, sad and reflective even a decade before his execution. And Thomas Cromwell looking like a pork butcher, watching to ensure his assistants are not over-generous in parcelling out his meat.

William Cecil has the hooded-eyed gimlet gaze of a politician who somehow survived under Edward VI, Mary, and then Elizabeth. The boy Edward radiates a chilling self-certainty at just the age of ten. And then there is Mary.

Hers is a portrait intended to flatter, commissioned in 1554 to convince Philip II that she was a marriageable prospect. Despite that, her strong fierce eyes — their darkness accentuated by the green tiles behind her — seem to look directly into the soul of the viewer. This is not a woman you would like to encounter in a dark alley.

It is a single intimidating image. Perhaps more informative are the successions of images of Henry VIII and Elizabeth I. In the 1520 portrait of Henry, where he is paired with Catherine of Aragon (a pair that she kept until her death), he looks weak and indulged by contrast to her strength and determination. But, by 1537, he strides like a colossus, arms and legs akimbo, in Holbein’s iconic image of power.

Equally revealing is the succession of Elizabeths. The earliest, from 1560 — thought to be an early tool in marriage negations that she skilfully conducted without conclusion for decades — shows her softer side. But later the famous Pelican brooch image suggests the self-sacrifice with which she sustained the nation. Then the manly resolution of the Armada portraits hint of “the heart of a king, and a King of England”. All document the skill with which she navigated the difficult waters of 16th-century queenship, when marriage was both solution and problem for questions of succession.

The excellent volume that accompanies the exhibition is full of fascinating detail — such as how Henry VIII attempted to undermine the popular reputation of England’s monasteries for charitable piety by passing the 1533 Buggery Act to enable a series of unevidenced smears about monkish impropriety. There are no portraits connected with that, which is perhaps just as well.