The many portraits painted by Pietro Aldi, which show his undisputed skill as a sensitive interpreter of the physical and psychological traits of his subjects, can be grouped into two types. One group contains works made on commission, perfectly finished, which portray relatives or authoritative personages of his time, like the Portrait of a Gentleman, Father Leonardo Aldi (both dated 1885), and the two pictures of a Young Man with a Beard.

Other portraits are studies for larger compositions and bear witness to the care the painter took in painting his favorite historical subjects: rapid oil sketches reserve the freshness of a quick notation, to be worked out more fully in the final phase of execution. Examples are the African Woman, Leonardo Coretti, and the Man Wearing a Hood, included in the Triumph of Judith (1887), or the Portrait of a Man used as a model for Michelangelo Painting in the Sistine Chapel (1884).