This painting could be fairly important not only because the artist is nationally recognized but because of the ancestry of the sitter.
According to Paul Heinegg, author of "Free People of Color in North Carolina," this Thomas Johnson, a wealthy Maryland planter, was none other than the great grandson of Anthony Johnson, one of the earliest African Americans to settle Virginia. And it is this very Anthony Johnson who is a pivotal figure in the debate over the origins of slavery.
Anthony Johnson had acquired close to a thousand acres of land by the middle of the 17th century and was among the first generation of free blacks whose relative affluence have forced scholars of the Colonial south to revise their original views on the origins of American slavery and the fine line between this "peculiar" institution and indentured servitude.
What makes Anthony Johnson a central figure in the debate is an utterly bizarre and "politically incorrect" twist of fate. From evidence found in the earliest legal documents extant, it is Anthony Johnson who we now must recognize as the nation's first slaveholder. After all, the court battle he eventually won in 1655 to keep John Casor (Ceasar?) as his servant for life, identifies this unfortunate soul as the first slave in the recorded history of our country. Claiming that he had been imported as an indentured servant, Casor attempted to transfer what he argued was his remaining time of service to Robert Parker, a white, but Johnson insisted that "hee had ye Negro for his life".
The court ruled that "seriously consideringe and maturely weighing the premisses, doe fynde that the saide Mr. Robert Parker most unjustly keepeth the said Negro from Anthony Johnson his master....It is therefore the Judgement of the Court and ordered That the said John Casor Negro forthwith returne unto the service of the said master Anthony Johnson, And that mr. Robert Parker make payment of all charges in the suit."
from: http://www.pbs.org/wgbh/pages/frontline/shows/secret/famous/johnson.html