The sitter was the eldest son of William Boyd, 4th Earl of Kilmarnock and his wife Lady Anne Livingstone, daughter and heiress of James, 5th and last Earl of Linlithgow and 4th Earl of Callendar, and his wife Lady Margaret Hay, daughter of John, 12th Earl of Erroll. His father, an ardent Jacobite, had led Prince Charles Edward's Horse Grenadier Guards at the Battle of Culloden (1746). He was captured and convicted of high treason and forfeiting the honours and estates of his family, on 18 August 1747, beheaded for treason on Tower Hill.
The sitter, born James Boyd on 20 December 1726, had opposed his father's Jacobite views and served in the Scot's Fusiliers at Culloden on the side opposed to his father, and eventually, in 1752, recovered the lands of Kilmarnock, which he afterwards sold to the Earl of Glencairn. In 1758, on the death of his great-aunt Mary, Countess of Erroll, James inherited the Earldom and became 15th Earl of Erroll, changing his surname from Boyd to Hay. In 1761, he officiated as Constable of Scotland at the Coronation of King George III. He married firstly on 15 September 1749, Rebecca (d. 1761), daughter of Alexander Lockhart, Lord Covington, by whom he had one daughter, Mary, who married General John Scott, of Balcomie. In 1762, he married secondly, Isabella, daughter of Sir William Carr of Etal, Northumberland, by whom he had several children, including George, who succeeded to the Earldom on 3 July 1778, and William, who became 17th Earl of Erroll on 14 June 1798. The Earl's grandson, William George, 18th Earl of Erroll was created Baron Kilmarnock in the peerage of the United Kingdom in 1831.
According to Reynolds's ledger, Erroll sat for his portrait in March and April in 1762. Although Reynolds records a fee for this portrait of 100 guineas, this bill was still outstanding at the Earl's death in 1778, and was only paid in 1783. Reynolds also painted the Earl's second wife, Isabella (1742-1808), firstly in 1759-61 (Worcester Art Museum, Massachusetts) and in peeress's robes, circa 1793 (Glasgow Art Gallery, Scotland).
The Earl was renowned for his great height and commanding presence. Horace Walpole, in a letter of 24 September 1761 to George Montagu, described him at King George III's coronation as 'one of the giants in the Guildhall', and Dr Johnson likened him to the 'Great Sarpedon', son of Zeus and a famous ally of the Trojans.
Viscount Lee of Fareham assembled an important collection of pictures soon after he retired from a successful political career in 1922. He had already presented his house, Chequers, to the nation in 1917. He was an adventurous and independently minded collector who made some outstanding purchases in the fields of eighteenth century British Art and pictures from the Italian Renaissance.