A half-length portrait, slightly to the left, showing the sitter in captain's uniform of the 1767–74 pattern. He is wearing a grey wig; sky forms the background. This portrait was acquired as a portrait of an unknown captain in 1935. It is one of five known versions. Another version, formerly in the collection of the Marquess of Lansdowne, bears a very old label on the back identifying the sitter as Captain (later Vice-Admiral) Sir Peter Denis (1713-78), and it was sold as such from the Lansdowne collection at Christie’s, London, on 7 March 1930 (lot 39). A third version, also identified as Denis, appeared in Glasgow in 1958.

Some time after 1961, two further versions were reported to the museum, one in the possession of Lord Crawford and the other with the Duke of Northumberland at Alnwick Castle. These two, however, were identified as portraits of Captain Sir Basil Keith, who died in 1777. Keith's name has been added as a later inscription on the Alnwick version and the museum also received advice from the Scottish National Portrait Gallery that the sitter was probably Captain Keith, but the evidence for this suggestion is not recorded.

Unfortunately, no other portraits of Denis or Keith are yet known to make comparisons. No photographs of the Crawford and Northumberland versions have yet been seen and the Glasgow portrait remains to be relocated.

Although the date is unconfirmed, Keith is reported to have been born in circa 1734. If so, he would have worn the uniform depicted in this portrait between the ages of about 33 and 40, but Denis would have worn it when he was 54 to 57. On the sitter's apparent age, therefore, the identification as Denis appears to be the more likely but the matter remains for resolution.

Nathaniel Dance, the artist who painted this portrait, worked with Pompeo Batoni in Rome, and on his return to London in 1765 achieved success as a portrait and history painter. In 1768, he joined a group of artists who successfully petitioned George III to establish the Royal Academy in that year.