Famous as one of Copley's finest works soon after it was painted, this portrait shows the artist at the height of his powers. Born in Boston in 1738 into a poor immigrant family, Copley was self-taught. He developed a highly finished style that rendered the features, costumes, and settings of his subjects with remarkable accuracy. Copley always kept a keen eye on his competition, and he may have been inspired to paint both Sarah and Thomas Mifflin on a single canvas by his contemporary Charles Willson Peale, who had recently completed a group portrait of the Philadelphia Cadwalader family that was admired for its portrayal of family unity and affection. Here, Copley depicts not only the features and costumes of his sitters with his famed skill, but creates an image of marriage as an affectionate, equal partnership--an innovative concept in American portraiture at the time.