Green’s Dictionary of Slang

(UK Und.) a money-lender who specializes in loaning money, often to gamblers, and then defrauding them by avoiding repayment when due, but rather entrapping them in a legal suit, the only resolution of which is the handing over not of the original loan, but of land or valuables that are worth much more.

1602		Dekker Satiromastix I ii: Ile shake the gull-groper out of his tan’d skinne.
1608		Dekker Lanthorne and Candle-Light Ch. 3: The Gul-groper is commonly an old Mony-monger, who hauing trauaild through all the follyes of the world in his youth, knowes them well, and shunnes them in his age.
1685		New plot newly discovered 4: The Gull-groper is one that is an old Money-monger.
c.1698		B.E. Dict. Canting Crew n.p.: Gull-gropers c. a By-stander that Lends Money to the Gamesters.
1725		New Canting Dict. [as cit. c.1698].
1737, 1759, 1760, 1776		Bailey Universal Etym. Eng. Dict. [as cit. c.1698].
1785, 1788, 1796		Grose Classical Dict. of the Vulgar Tongue.
1801		‘Modern Dict.’ in Sporting Mag. May XVIII 100/2: Gullgropers.—Usurers who lend money to gamesters.
1811		Lex. Balatronicum.
1823		Egan Grose’s Classical Dict. of the Vulgar Tongue.