Alfred Reckendrees said:  
> I don't know whether he was the first, but  
> Karl Marx: Critique of Political Economy (1859)  
> used the term.  
  
  
Hmmm, the reference to Marx (the term, incidentally, appears in the    
1857 Introduction) opens the thorny problem of whether the    
translation from German is correct. This seems to be another case of    
translation in "economicist" language of Marx's original terms, which    
were "Agenten der Produktion" (http://www.mlwerke.de/me/me13/   
me13_615.htm). This was correctly translated into Italian as "agenti    
della produzione".  
  
My experience is that Marx's translation into English is at places    
extremely inaccurate, and should always be double-checked before    
being used.  
  
Daniele Besomi