George III's accession is therefore being celebrated in a number of institutions, whether "Half Term Madness" at York Castle Museum or special lectures in the Historic Royal Palaces. In London we are constantly reminded of him through Buckingham Palace, the house which he acquired as the monarch's London residence, and through the magnificent King's Library built in 1828 to house his books, which is now the Enlightenment Gallery of the British Museum. The books themselves are displayed in a spectacular glass tower in the entrance hall of the nearby British Library, and a marble bust of him sculpted in 1812 stands in front of the tower. In South Kensington his instruments of experimental philosophy are shown in a dedicated gallery on the third floor of the Science Museum.
More parochially, his bouts of ill-health make him especially interesting to an institution such as the Wellcome Library which views the history of health as the central strand in its perspective on history. Alan Bennett's popular play (1991) and film (1994) The madness of George III was inspired in part by work at the Wellcome Institute by Roy Porter, Bill Bynum and Michael Neve (which, in George III 's case, in turn built on earlier research by Richard Hunter and Ida MacAlpine): Michael Neve suggested it would be a good subject for a play and lent Bennett some literature on the subject. 
There are many representations of the king in the Wellcome Library. Among several intimate portraits which focus on the king as a person, the mezzotint from a portrait by Thomas Frye shown above (top: Wellcome Library no. 25552i) portrays him in 1762, two years after his accession: squared up for transfer, it would be suitable as a model for an inn-sign of the King's Head. If we wish to test its accuracy against an independent control, we can compare it with this etching after a rapid sketch by Nathaniel Dance (1735-1811): the basic physiognomy is the same, though being drawn some thirty eventful years later, demonstrates the rejuvenation that tends to be involved in royal, but not only royal, portraiture.
Wellcome Library no. 570646i
King George III suffered several extended periods of illness involving mental breakdown, the first being in 1765 when he described himself as "a mind ulcer'd by the treatment it meets with from all around". Another lasted from the summer of 1788 to the spring of 1789. To celebrate his recovery in 1789 two prints shown here were published.
A mezzzotint attributed to James Parker (left: Wellcome Library no. 27217i) shows "The triumph of Hygiea [Hygieia]. From a transparency of the happy recovery of the KING, March the 10th 1789, exhibited at Lord Howard de Walden's". In a transparency, extra elements are revealed when the work is lit from behind: when lit by Lord Howard de Walden's lanterns, did the clouds disappear and a radiant sun take their place in the upper left part?
Wellcome Library no. 42665i
However, George III had plenty to agitate his mind during his career. The King of France was guillotined in 1793, and in the previous year Gustaf III, King of Sweden, had been assassinated by his political opponents. In this caricature by James Gillray, the King and Queen Charlotte are disturbed at their toilet when William Pitt rushes in to bring "news from Sweeden": "Another monarch done over!". The horrified King stammers: "What? Shot? What? What? What? Shot! Shot! Shot!", showing the habit of repeating words in rapid succession which features memorably in Alan Bennett's play as a sign of the King's recovery of his personality.
Further episodes of mental disturbance occurred in 1801 and 1804. The king's fiftieth anniversary was celebrated on 25 October 1810 with a reception at Windsor, but it seems to have precipitated the insanity which persisted until the end of his life. After this date the king was in confinement: the portraits were presumably either speculative or based on existing portraits. Two from this period show him as a King Lear-like figure, blind, bearded and lost to the world: one by Charles Turner, the other possibly by John Jackson: the latter (right) was published as a mezzotint immediately after his death on 29 January 1820. It was "published by His Majesty's most gracious permission": that must mean George IV.
Right: mezzotint by S.W. Reynolds, 24 February 1820. Wellcome Library no. 569597i
Wellcome Library no. 23324i
In the shadow to left lurks the young woman who hands out the beakers of water. The Union flag flies on the pavilion roof. The king is alert and looks vigorous. Alas, the Cheltenham water did not preserve his health, but from the nine portraits of the king shown above (selected from a much larger number in the Library), this happier portrait would be the writer's choice for the Wellcome Library's Item of the two hundred and fiftieth October since George III's accession. What what what's yours?
For a survey of the iconography of George III see John Ingamells, Mid-Georgian portraits, 1760-1790, London: National Portrait Gallery, 2004, pp. 195-203
 Alan Bennett, The madness of George III, London 1995, p. viii