The Dictionary of American Slang says it's been around since about 1895 but gives no further explanation of its origin. The name John and its relatives (Jacques, Jack, Johnny . . . ) turn up in many phrases to mean an unspecified male, as in John Doe. JOHNNIE -- "Johnnie meant fellow, chap in English by the 17th century and a man-about-town in the 1880s. 'Johnny-Come-Lately' was in use in America by the 1830s. 'Johnny-on-the-spot' by the 1890s and 'stage-door Johnny' by 1912.'" From "John and Mary:Common First Names," a chapter in "Listening to America" by Stuart Berg Flexner (Simon and Schuster, New York, 1982). Johnny-on-the-spot is a noun that means "an unusually alert fellow who is capable of decisive action, seizing an opportunity, etc. Also (obs.) 'Johnny-on-the-job.' 1896 Ade 'Artie' 19: She was settin' over in the corner, and a Johnny-on-the-spot, with a big badge, marked 'Committee,' was tryin' to keep cases on her. Ibid. 63. I'll be Johnny-on-the-spot to see that everything's on the level.'" From the "Random House Historical Dictionary of American Slang, Volume 1, H-O" by J.E. Lighter, Random House, New York, 1994.
Etymology is the opposite of Antipodes
The study of word origins is called etymology. In my student days I was told that it is one of the less exact areas of historical linguistics.
◘ life; etymology
What is the etymology of the word persecute its for my language homework
Given the conflicting evidence, linguists could not agree on the etymology of the word.
Johnny-on-the-Spot - 1919 is rated/received certificates of: USA:Approved
Johnny on the Spot - 1912 was released on: USA: 23 October 1912
Johnny-on-the-Spot - 1919 was released on: USA: 17 February 1919
The cast of Johnny Off the Spot - 2008 includes: Konstantine Anthony as Dracula Jeff Croghan as Pedestrian George Retelas as Johnny
The Tycoon - 1964 Johnny on the Spot 1-24 was released on: USA: 2 March 1965
The etymology of etymology is from the greek etumologia which means "true sense of a word"
Philip Sheridan has written: 'Johnny on the spot'
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On The Spot Johnny Wright's Quest for the Next Supergroup - 2011 Style 1-6 was released on: USA: 11 March 2011
Etymology is the opposite of Antipodes
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On The Spot Johnny Wright's Quest for the Next Supergroup - 2011 Welcome to Hollywood 1-14 was released on: USA: 6 May 2011