A short thick man or woman. Norfolk dumpling; a jeering appellation of a Norfolk man, dumplings being a favourite kind of food in that county.
From the British Museum description:
A whole length satirical portrait of the Duke of Norfolk, directed to the right; in his left hand is the baton of Earl Marshal; his right hand is in his waistcoat pocket. He wears top-boots, a slouched hat, and his hair is closely cropped. Earlier caricatures show the Duke wearing his own hair without powder, hanging on his neck. 21 September 1791
Slang term taken from the 1811 Dictionary of the Vulgar Tongue.