Green’s Dictionary of Slang

(US/Aus.) one who does not give up; a hard worker.

1900		E.H. Babbitt ‘College Words and Phrases’ in DN II:i 50: plugger, n. A hard student.
1904		Number 1500 Life In Sing Sing 251: Plugger. Energetic worker.
1904		Sydney Sportsman (Surry Hills, NSW) 25 May 1/5: [of a racehorse] [A] cut-throat race [...] allows a ‘plugger’ to cop .
1921		Cleveland Enterprise 4 June 1/3: Everybody out here is a booster and plugger for one common purpose [DA].
1928		R. Carr Rampant Age 19: Being a heavy-jawed plugger [...] he had forged steadily ahead.
1949		Monteleone Criminal Sl. (rev. edn).
1952		G. Meek ‘The Ringer’ Station Days in Maoriland 104: Then just crack up like an ice crust while the pluggers fought for more.
1959		M. Richler Apprenticeship of Duddy Kravitz (1964) 168: Lennie had a rep for being a plugger.
1967–8		Baker et al. CUSS.
1996		J. Byrell Lairs, Urgers & Coat-Tuggers 331: Usually the types who take out the rich old race are good old pluggers.