Green’s Dictionary of Slang

fiddler n.²

a coachman.

1819		P. Egan Key to the Picture of the Fancy going to a Fight 9: The drag Fiddler can toss off a quartern of ‘Max’ without making a wry mug.
1821		Egan Life in London (1869) 74: He was a perfect hero with the whip; a first-rate Fiddler.