Harry B. Wehle. The Metropolitan Museum of Art: A Catalogue of Italian, Spanish, and Byzantine Paintings. New York, 1940, p. 166, as "Portrait of a Knight," by an unknown north Italian painter, late sixteenth century.
Federico Zeri. Unpublished catalogue entry. late 1960s, identifies the sitter as Alfonso I d'Este; attributes it to an unknown Ferrarese painter, calling it probably an almost contemporary copy after a lost original by Dosso or Battista Dossi; states that the composition seems to be derived from Titian's second portrait of the sitter (lost).