Green’s Dictionary of Slang

1. (UK/US Und.) a major criminal.

1910		J. Sullivan ‘Criminal Sl.’ in Amer. Law Rev. LII (1918) 890: The stylish hotel beat is called a ‘baron.’.
1925		Sheboygan (WI) Press 25 Sept. 1/2: Dressed in a close fitting grey suit, the dapper ‘beer baron’ related a story of the traffic in privileges inside [...] the old prison.
1928		Phila. Eve. Bulletin 5 Oct. 40/3: Here are a few more terms and definitions from the ‘Racket’ vocabulary: [...] ‘baron,’ a leader of a group of bootleggers.
1934		F. Tuohy Inside Dope 207: Importers [of drugs], big and important as they are, do not constitute the ultimate hierarchy of the traffic. There are others higher up still: the ‘C’s’, the so-called ‘Drug Barons’. [Ibid.] 207: A selection of ‘barons’ have been arrested spasmodically in recent years.
1942		P. Wylie Generation of Vipers 134: There were some Jewish gangsters [...] but there were shanty Irish rum barons.
1950		Goldin et al. DAUL 146/2: Number-baron. A powerful and wealthy operator in the policy numbers game.
1960		C. MacInnes Mr Love and Justice (1964) 30: For the vice barons: the gaff landlords and [...] the easy-money boys.
1961		J. Sparks Burglar to the Nobility 131: Any tearaway who is seeking a reputation dreams of being able to find a well-established baron who has suddenly gone milky, and will then seek to do him up.
1972		P. Fordham Inside the Und. 111: The barons of the American underworld scene.
1978		L. Kramer Faggots 19: [He] had been a beer baron.
1981		N. Farki Countryman Karl Black 137: Him is a land-baron, a backra man.
1999		Guardian G2 31 May 17: Gillian is a hooker run by a local drug baron.
2000		Observer Rev. 2 Apr. 1: Britain’s own narco-baron, Curtis Warren, now serving a long stretch in a Dutch prison.
2002		J. Cameron Hell on Hoe Street 121: Rameez was a kind of baron. Kind of a minor baron. He did local business, protection and retail, and a bit of car theft.

2. anyone who has money.

[1841		N. Carolina Standard (Raleigh, NC) 23 June 4/1: Billy Barlow — A New Rag — Currency Song. [...] A real rag-baron is Billy Barlow / Oh! dear, raggedy Oh!].
1911		Day Book (Chicago) 11 Dec. 4: [photo caption] This picture was snapped at federal court [...] two of the ten indicted beef barons.
1933		W. Scott ‘Take ’Im Alive’ Und. Mag. May 🌐 Greetings, Hardhead. Going to shell out like a beer baron on a souse, eh?
1938		X. Herbert Capricornia (1939) 221: He hoped to live the rest of his life as a beef-baron.
1984		(con. WW2) T. Jones Heart of Oak [ebook] The only time that it was possible to feel what civilians call ‘comfort’ was[...] when a few of the matelots went ashore, if they had any money, or if there was a baron in line to be strangled.
1986		S. King It (1987) 868: The other members of the Board are the descendants of lumber barons.

3. (UK prison, also snout baron, tobacco baron) an influential convict within a prison, esp. one who trades in tobacco or drugs.

1948		Sun. Mirror (London) 29 Aug. 6/5: And so a prison black market has arisen. A race of ‘tobacco barons’ has grown up [...] endeavouring to rule the roost behind the backs of the warders.
1948		People 31 Oct. 2/1: Ninety per cent of prison corruption [...] can be traced to the illicit traffic in tobacco [...] And every gaol has its ‘snout baron’ — the little Al Capone who has the racket nicely sewn up.
1950		P. Tempest Lag’s Lex. 10: Briefly, a baron is one who always has plenty of money and/or tobacco.
1956		‘Charles Raven’ Und. Nights 100: Ten free cigarettes – much to the annoyance of the snout barons. [Ibid.] 138: Soon Charlie was established as the leading tobacco boss, or Snout Baron, in the prison.
1958		F. Norman Bang To Rights 23: If people can’t be barons without going around punching little geezers up in the air.
1967		G.M. Williams Man Who Had Power Over Women 206: Stick your fags down your socks [...] You’ll be a snout baron.
1968		A. Burgess Enderby Outside in Complete Enderby (2002) 300: Slops out. Here’s your skilly, you horrible murderer, you. Snout-barons.
1971		Listener 86 348: There is Garvey, snout baron and hard man; ‘Spasm’ Horricks, the epileptic sucker-up [etc.].
1980		S. McConville ‘Prison Lang.’ in Michaels & Ricks (1980) 525: Tobacco may expensively be borrowed or bought from a baron.
1984		‘Derek Raymond’ Devil’s Home on Leave 95: You’re a snout baron [...] seems you’ve been in front of the governor for working a few tabs in.
1989		P. Manning ‘Sl.’ in Kray (1989) 62: And because silence was the rule and talking was out; / Tobacco barons in prisons called tobacco snout.
1998		J. Hoskison Inside 142: ‘Don’t let me ever catch you smiling at a screw again,’ said one of the drug baron’s henchmen.
1999		R.G. Barrett Wind & Monkey (2013) [ebook] The drug baron was his next door neighbour [...] he’d just walked out on the balcony smoking a skinny joint.
2006		B. Matthews Intractable [ebook] Tobacco barons reigned in each wing of the prison.
2007		M.J. Hyland This Is How 194: ‘Here comes the snout-baron,’ says Stevenson. [...] ‘If you need any snout,’ he says, ‘you see me’.
2008		(ref. to 1971) F. Dennis ‘Old Bailey’ Homeless in my Heart 179: Beginning to learn what is meant / By a ‘jolt’ or ‘toad in the hole’, / By ‘Baron’; or ‘dint’ or a ‘dunt’.
2013		K. Sampson Killing Pool 53: From small-time hoister to big-time charlie baron.