Green’s Dictionary of Slang

gagger n.1

[gag v.]

1. a confidence trickster, a cheat, esp. when telling ‘sob-stories’ or posing as a deaf-mute.

[UK]J. Messink Choice of Harlequin I viii: Though you’re a flashy coachman, here the gagger holds the whip.
[UK]Whole Art of Thieving 34: Gaggers [...] They are a very deceitful set of people in general, that deserve a prison more than relief: some of them go in a sailor’s dress, pretending that they were galley slaves, and that their tongues were cut out by the Turks, and their arms were burnt in the row gallies: to deceive the world they cut the strings of their tongues, and so swallow it down their throat, that none can perceive it, and make their arms raw by perpetual blisters; but if they were taken to the whipping post, the dumb would speak, and those that walk with crutches would shift without them.
[UK]Grose Classical Dict. of the Vulgar Tongue ms. additions n.p.: Gaggers. High and Low. Cheats, who by sham pretences, & Wonderful Stories of their sufferings, impose on the Cedulity of well meaning People.
[UK]Grose Classical Dict. of the Vulgar Tongue (3rd edn) .
[UK]Lex. Balatronicum [as cit. 1796].
[UK]Egan Life and Adventures of Samuel Hayward 50: An hotel [...] distinguished for its life and fun, and visited by all the rum customers upon the pavé, from the four-in-hand whip to the neddy proprietor—traps, gaggers.
[UK]Sussex Advertiser 14 Apr. 4/3: [We] soon passed a long string of gaggers, priggers, Adam Tylers, fancy coves, autum [sic] morts, gammoners, sweetners, uprightmen, bully huffs, lully priggers, star gazers, and coves of all sorts.
[UK]G. Kent Modern Flash Dict.

2. a joker; in theatrical context, esp. of comedians, one who ad-libs.

[UK]Punch I 69: Men with ‘swallows’ like Thames tunnels, in fact accomplished gaggers and unrivalled ‘wiry watchers’ [F&H].
[UK]Era 9 July 15/3: Actors in those days — especially those who played comic parts [...] were incorrigible ‘gaggers’.
[UK]Globe (London) 3 Mar. 1/4: The low comedy was much toned down [...] In other words, the gaggers were gagged [F&H].
[UK]Era (London) 13 Jan. 9/5: He was a great ‘gagger,’ and gagged through all his speaking parts.
[UK]‘Ian Hay’ First Hundred Thousand (1918) 106: The punctilious Mucklewame was still glaring severely after this unseemly ‘gagger’.
[UK]Eve. Teleg. (Dundee) 5 Nov. 4/3: [headline] Stage Gaggers who made History. Impromptu Lines in Famous Plays.
[UK](con. 1860s) P. Ackroyd Dan Leno and the Limehouse Golem 78: She might make a good gagger.

3. a tramp, a beggar, who uses ’true’ stories to enhance the basic beggar’s entreaties.

[UK]Leicester Chron. 21 June 12/2: ‘Tom the Gagger‘ introduced Fred to a company of seven others.
Derbys. Advertiser 2 Dec. 25/4: ‘Gaggers,’ the higher class of treamps, with their plausible tales.
[UK]Leamington Spa Courier 20 Sept. 7/1: There are a great many tramps staying in this district at the present time [...] We have among us ‘gaggers’ (beggars).
[UK]‘George Orwell’ Down and Out in Complete Works I (1986) 176: These (omitting the ones that everyone knows) are some of the cant words now used in London: [...] A gagger – beggar or street performer of any kind.

4. (US Und.) a receiver of stolen goods.

[US]Monteleone Criminal Sl. (rev. edn).

5. (US tramp) a tramp who makes a living by telling stories.

[US]F.O. Beck Hobohemia 47: Some of his associates are ‘gaggers’ who get their living — a scanty one — by telling tales.