As in the case of Mrs. Siddons, Grimaldi does not actually make an appearance in
Deception. He is mentioned, however, in an unflattering comparison to the hero's mother, Lady Greville. Unflattering to her, that is.
Born in 1778 to the ballet master at Drury Lane and one of the ballet dancers, Joseph Grimaldi grew up in the very life he went on to pursue. At the age of three he performed on stage at Sadler's Wells theatre. Much later, he fell in love with and married the theatre owner's daughter, who died in childbirth 18 months later.
Grimaldi made the clown the central character of the British Harlequinade. His greatest success was
Harlequin and Mother Goose at Covent Garden. It debuted in 1806 and ran for 92 nights, taking in £20,000. He was considered the first "clown" and is honored as such to this day.
He retired in 1828 and died in 1837 at the age of 58.
*Further reading: Wikipedia; Joseph Grimaldi at Its-Behind-You.com
**Portrait done by John Cawse in 1807. Second illustration of Grimaldi as a clown was done c.1820.