Short answers, pulled from the story.
Sir James Thornhill (the 25th of July 1675 or 1676 - the 4th of May 1734) was an English painter of historical subjects working in the Italian baroque tradition. He is best known for painting the Painted Hall at the Royal Hospital, Greenwich, the interior of the dome of St Paul's Cathedral, and works at Blenheim Palace, Chatsworth House, Hampton Court Palace, and Wimpole Hall.
Yes. George I knighted Thornhill on the 2nd of May 1720, making him the first native-born artist in England to receive a knighthood. In the same year he was appointed Serjeant Painter and served as master of the Painters' Company.
Thornhill was awarded the St Paul's commission on the 28th of June 1715 by a Whig, low-church dominated committee. The Archbishop of Canterbury, Thomas Tenison, reportedly insisted the painter be both a Protestant and an Englishman, conditions that directly supported Thornhill over foreign competitors. The eight scenes he painted between 1716 and 1719 depict episodes from the Life of St. Paul, executed in grisaille.
The Painted Hall at what is now the Old Royal Naval College is a large-scale allegorical scheme of wall and ceiling decorations. Thornhill received the commission in 1707 and completed it in 1727, a span of twenty years. The program depicts the Protestant succession of English monarchs from William III and Mary II to George I.
William Hogarth appears to have been a member of Thornhill's free drawing academy in Covent Garden from its founding in November 1724. On the 23rd of March 1729, Hogarth married Thornhill's daughter Jane. Thornhill and Hogarth also visited Sarah Malcolm together in Newgate Prison, just days before her execution, so Hogarth could paint her portrait.
Thornhill's copies were auctioned by Christopher Cock on the 24th and the 25th of February 1735 at the Great Piazza, Covent Garden. John Russell, 4th Duke of Bedford bought the full-size copies for £200, a price noted as less than the cost of materials. In 1800, Francis Russell, 5th Duke of Bedford presented them to the Royal Academy of Arts in London, where they remain.