Green’s Dictionary of Slang

billy barlow n.¹

a fool.

[1831		Quizzical Gaz. 27 Aug. 6/1: Sure everyone alive must know / The celebrated ‘Billy Barlow’ / [...] / And ‘Billy’ though he went to school, / Was always call’d the ‘village fool’].
1835		Morn. Post (London) 22 Oct. 4/4: ‘Billy Barlow’ The above ecentric individual, whose real name was John Clarke [...] was found on Monday morning in a dying condition.
1841		N. Carolina Standard (Raleigh, NC) 23 June 4/1: Billy Barlow — A New Rag — Currency Song. We’ll have rags and rag money, and Billy Barlow! [...] So hurra! for the ‘shinnies’ of Billy Barlow.
1859, 1860		Hotten Dict. of Modern Sl. etc.
1861		(con. 1840s–50s) H. Mayhew London Labour and London Poor III 138/1: ‘Billy Barlow,’ is another supposed comic character.
1864, 1867, 1870		Hotten Sl. Dict. 74: billy-barlow a street clown [...] Billy was a real person, semi-idiotic, and, though in dirt and rags, fancied himself a swell of the first water. Occasionally he came out with real witticisms. He was a well-known street character about the East-end of London, and died in Whitechapel Workhouse.