Green’s Dictionary of Slang

1. an amusing companion, a ‘wag’.

1600		Shakespeare Twelfth Night I v: A plague o’ these pickle-herring! How now, sot!
1694		J. Crowne Married Beau IV i: I don’t know what I am now; a Pickleherring, I think. I’d be loath to meet with a hungry Dutch Seaman.
1711		J. Addison Spectator No. 47 n.p.: There is a set of merry drolls... whom every nation calls by the name of that dish of meat which it loves best. In Holland they are termed pickled herrings [F&H].
1859		Hotten Dict. of Modern Sl. etc. 74: ‘A pickle herring,’ a comical fellow. [...] Old.
1864, 1867, 1870		Hotten Sl. Dict. [as cit. 1859].

2. (also pickle-her-ring) a professional clown, usu. one who accompanies an itinerant quack doctor.

1702		in J. Malcolm Anecdotes of Manners and Customs (1808) 313: The stage was now overrun with nothing but Merry Andrews and Pickle-her-rings.
1785, 1788, 1796		Grose Classical Dict. of the Vulgar Tongue n.p.: Pickle [...] pickle herring, the zany or merry Andrew of a mountebank.
1811		Lex. Balatronicum.
1822		W. Scott Peveril of the Peak II 199: I mean a rope-danzer, a mountebank, a Hans pickel-harring. I vas know Adrian Brackel vell—he sell de powders dat empty men’s stomach.
1859		Hotten Dict. of Modern Sl. etc. 74: ‘A pickle herring,’ [...] a merry Andrew [i.e. a clown].
1864, 1867, 1870		Hotten Sl. Dict. [as cit. 1859].
1899		Dublin Wkly Nation 17 June 11/6: He is intentionally a buffoon, jester [...] or pickle-herring.