Alexander Keith (1705-1792) was one of the founding members of the Royal Society of Edinburgh. He was an under clerk in the court of session and his father purchased an estate at Ravelstoun, East Lothian, in 1726 from Sir Archibald Primrose of Dunipace, Bt.
Alexander Keith's father claimed descendancy from the Keiths of Pittendrum, Aberdeenshire and the Earls of Marischal, a claim perpetuated when the former purchased the estate at Dunnottar from the last Earl Marischal in 1766.

Another version of this portrait is in the Collection of Brigadier Swinton of Kimmerghamme.