The obscure artist Pieter Koets (also referred to as J. Pieter Koets) remains a mystery as nothing specific about his life is known except for his active period between 1717-1743 and being active in Amsterdam ca. 1739-1740  as a painter of portraits. The present fully signed portrait of a man of middle-age wearing a pointed hat in black crayon on blue prepared paper is possibly a self-portrait.
Only a very small number of half-length portrait paintings in oil on canvas, all dated between 1717 and 1740  is known today and works on paper by his hand are exceptionally rare.
 Pieter A. Scheen, Lexicon Nederlandsche Beeldende Kunstenaars 1750-1950. Kunsthandel Pieter A. Scheen N.V. 's Gravenhage. 1969. p. 622.
 Half-length portrait of Arnoldus Gelderman, dated 1723, major of Zwolle and his wife Petronella Unger (pendant). Private-collection. Half-length portrait of Samuel Johannes Gelderman, dated 1732, and his wife Engelina Johanna Kymmell (pendant). Private-collection.