Although the subject is not identified in the Mahockney portrait, our research strongly suggests that it is a previously uncatalogued portrait of John Tyler, 1790-1862, Governor of Virginia (1825-27), U.S. Senator, and tenth President of the United States (1841-1845).
Below are side-by-side comparisons with known portraits and daguerreotypes of John Tyler during his career – with the Mahockney portrait on the right in each pair:
Tyler portrait by John Wesley Jarvis, 1826; painting has remained within the Tyler family, reproduction below in John Wesley Jarvis, American Painter, 1780-1840. With a Checklist of His Works (New York Historical Society, 1949):
Tyler portrait circa 1842 by G.P.A. Healy: