Alessandro Algardi made this sketch model in preparation for a marble bust of Cardinal Paolo Emilio Zacchia (1554-1605), now in the Museo Nazionale del Bargello in Florence. Algardi left the marble version unfinished at his death in 1654. This suggests that this model was one of his last works. An assistant, possibly Domenico Guidi, subsequently completed the marble, which was owned by the Cardinal's niece, the Marchesa Rondanini. The marble lacks the vivacity of this terracotta, the handling of which is particularly remarkable given that the sitter died nearly 50 years before it was modelled. Algardi presumably based his work on an existing portrait.

The Cardinal, wearing a biretta (a three-cornered hat) and mozetta (a short hooded cape), is shown turning the pages of a book. This pose alludes to his written works, which included a treatise on the Immaculate Conception. This belief held that the Virgin Mary was conceived free of the stain of original sin. It later became a dogma of the Roman Catholic Church. Cracks are clearly visible throughout the terracotta, which were caused by firing the clay too quickly.