"Old Crump" was a real, and particularly colorful person associated with Cromwell--this from ancestry.com:

First you must meet John "Crump" Dutton, grandson of Thomas Dutton the
first owner of the Sherborne estate. John "Crump" was a hunchback, engaging,gregarious, wealthy, hard living, colorful, with a passion for gambling! A favorite legend tells of a card game in which Crump wagered Sherborne itself! Fortunately a faithful butler heard the cry "Sherborne is up!" and was able to restrain Crump's folly by lifting him bodily out of his chair and carrying him out of the room! During England's Civil War, 'Crump'contrived to be on both sides at the same time! At one point he offered to lend Charles I 50,000 pounds! By the end of the Civil War he had re-established friendly relations with Oliver Cromwell and even attempted to arrange a marriage between his nephew and heir with Cromwell's daughter!