A negro slave, noted for his fidelity, piety, and the faithful discharge of all his duties. Being sold, he has to submit to the most revolting cruelties. (Mrs. Beecher Stowe: Uncle Tom's Cabin.)
This tale was founded on the story of Josiah Henson (1787), told to Mrs. Stowe by Henson himself.
Source: Dictionary of Phrase and Fable, E. Cobham Brewer, 1894
More on Uncle Tom from Infoplease: