Believed to be a Portrait of David Walker (ca. 1830) (2009) references the style of 19th century stately portraiture. In place of the image of an aristocrat or king, Marshall portrays a black person as his protagonist, in three-quarter profile, wearing a military-like costume.

According to the title, the subject might be David Walker, a key figure in the struggle to abolish slavery in America. His mother was born free, but his father - who died prior to Walker's birth - was a slave. Though Walker had free status by grace of his mother, he was witness to slavery's cruelties. In 1829, Walker published his famous pamphlet Walker's Appeal in Four Articles; Together with a Preamble, to the Coloured Citizens of the World, but in Particular and Very Expressly to Those of the United States of America. In this emotional text, with well-chosen expletives, he urged slaves to rise up against their masters, regardless of the great risk involved.