This portrait was referred to in John Custis’s 1733 will. He left it to his son Thomas as “his grandfather’s picture.” John Custis (ca. 1703-1733) was the son of Thomas Custis and Elizabeth Custis. Thomas Custis (ca. 1684-before 1721) was the son of Edmund Custis (d. ca. 1700). Elizabeth Custis was the daughter of John Custis (ca. 1654-1714). The subject could be Thomas or John Custis.
Reference: John Custis (ca. 1703-1733), left to his son Thomas, “his Grandfathers Picture & the rest of the Pictures hanging in the hall.” Northampton County Wills, Deeds, etc., 1725-1733, no. 18, p. 260.