The portrait of Heinrich Schwarzwald IV (1619–1672) was incorporated into the PAS Gdańsk Library’s collection back in 1832. Heinrich Schwarzwald IV was the founder of the book collection for the Petrischule in Gdańsk. The oil painting on canvas in a period frame with no signature was painted in the mid–1600s. Both the book collection and the portrait were actually donated to the school at St. Peter and Paul Church after the death of Heinrich Schwarzwald IV’s nephew, Heinrich Schwarzwald V, in 1708. For a long period of time the uncle’s merits were attributed to the nephew due to the same names. In 1860 Gotthilf Löschin identified the real founder of the above mentioned library. The article, in turn, settles down the matter of the identification of the portrayed person. The painting was presumably painted by Andreas Stech (1635–1697). The source data confirm the mutual contacts between the painter and Heinrich Schwarzwald IV. Before being donated to the library, the painting underwent an intensive and thorough restoration performed by Franz Joseph Manskirch in the 1820s.