Green’s Dictionary of Slang

(US, orig. police) an influential sponsor or patron.

1932		‘Speech in the Post Office’ AS VII:4 278: Rabbi, one who aids in the securing of a special privilege or favor.
1939		L.M. Limpus Honest Cop 37: Each ambitious cop should have a ‘Rabbi’—a politician of some sort—a Tammany captain or district leader, or perhaps an Assemblyman, State Senator, or Alderman. Such a sponsor would look after the interests of his protégé.
1957		‘Ed Lacy’ Lead With Your Left (1958) 89: I thought about visiting Uncle Frank, asking him to talk to his ‘rabbi,’ as the boys called the club leaders.
1969		New Yorker 3 May 64/2: I asked him if he had done any thinking lately about [...] violence [...] ‘Mitch Ginsberg has been my rabbi in that,’ the Mayor answered .
1971		R.D. Pharr S.R.O. (1998) 520: ‘A rabbi, my square friend, is the name given to any important politican [...] your application [...] will never be processed unless you get a rabbi to light a fire under someone downtown’.
1986		C. Stroud Close Pursuit (1988) 148: Guy’s not with anybody outside, but he’s got a rabbi downtown. [Ibid.] 217: Kennedy [...] speculated from time to time and in a disinterested way about the identity of Wolfie’s ‘rabbi’ or ‘angel.’.
1997		G.V. Higgins Change of Gravity [ebook] ‘What if one of these bozos gets mad, what if he gets really mad? What if he goes to his rep, to my rabbi?’.
2000		G.V. Higgins At End of Day (2001) 6: Brian G’s his original rabbi — unless it was Moses.
2003		Simon & Alvarez ‘Backwash’ Wire ser. 2 ep. 7 [TV script] But if the case does come together, I would at least have Rawls as a rabbi.
2012		C. Stella Rough Riders 17: Sharpetti was the son of Eddie’s former street rabbi with the Vignieri crime family.
2017		D. Winslow The Force [ebook] He has rabbis at the Puzzle Palace [i.e. NYPD HQ], brass looking out for his interests.