Green’s Dictionary of Slang

1. the genuine article, the real thing.

[1745		Newcastle Courant 6 July 4/3: [book title] Simon Pure Unmask’d or the Errors of Quakerism].
1815		(con. 18C) Sir W. Scott Guy Mannering (1999) 345: Here [...] is the real Simon Pure--here’s Godfrey Bertram Hewit.
1825		Morn. Chron. (London) 26 Feb. 4/2: ‘We had indulged the hope that we had nearly completed the anatomy of “the real Simon Pure”’.
1835		Eve. Star (N.Y.) 1 May 2/2: We have just received Fanny Kemble’s Journal the real simon pure, and sure enough it is a ‘screamer’ to judge by a hasty glance.
1838		‘Uncle Sam’s Peculiarities’ in Bentley’s Misc. IV 48: Philadelphia had attracted none but the real Simon Pures, Obadiah Broadbrims, and Grey Susannahs.
1839		C.J. Lever Harry Lorrequer 137: Fearing every moment the arrival of the real Simon Pure should cover me with shame and disgrace.
1845		D. Corcoran Pickings from N.O. Picayune (1847) 137: The officer then commenced putting the question to the prisoners [...] till he came to the real Simon Pure.
1855		Newcastle Guardian 7 Apr. 3/3: [headline] The Simon Pure of the Journal.
1861		Bell’s Life in Sydney 15 June 3/2: He, ‘dusky as night,’ could not be the real Simon Pure.
1864, 1867, 1870		Hotten Sl. Dict. 291: Simon Pure ‘the real SIMON PURE,’ the genuine article.
1875		Burroughs Winter Sunshine 21: The fish-crow, whose helpless feminine call contrasts strongly with the hearty masculine caw of the original Simon [DA].
1885		Bulletin (Sydney) 18 Jul. 9/2: It is very seldom, when you call at a newspaper office, that you do see the editor. A presentable person is generally ‘put up’ in his stead, while the ‘real Simon Pure’ is fast asleep in the coal-hole. We substituted, in this office, […] the man who ground the ink. And he took well, too.
1893		Huddersfield Chron. 21 Oct. 5/7: I am the only Simon Pure / I am above all error.
1895		C. Crowe Aus. Sl. Dict. 74: Simon Pure, good money.
1908		G. Seagram Bushman All 19: Dick Carter of Cunnamulla, the real Simon Pure, at your service.
1909		L.W. Payne Jr ‘Word-List From East Alabama’ in DN III:v 370: Simon pure, adj. Genuine, true. Sometimes used as a noun. ‘He’s the Simon pure.’.
1922		Exeter & Plymouth Gaz. 28 Dec. 4/1: When the Simon Pure is discovered as leader, Mr Macdonald will be invited to walk.
1926		Wood & Goddard Dict. Amer. Sl.
1940		O. Strange Sudden Takes the Trail 215: It can’t be shown I ever saw Jesse Sark, and when you came to me, knowing all about him and his affairs, why shouldn’t I accept you as the real Simon Pure?

2. poteen.

1870		Mercury (Hubart) 23 Apr. 2/5: [from the Stranraer Free Press] [...] Athol brose, infernal compound, Simon Pure .
1908		L. Doyle Ballygullion 192: This is the rale Simon Pure this time.