Green’s Dictionary of Slang

1. (orig. US police/Und.) a criminal (or ‘civilian’) who works alone, not necessarily a recluse, but not permitting anyone to penetrate their façade [thus SE use, a solitary person, usu. male].

1909		F.H. Tillotson How I Became a Detective 130: Occasionally the police run across Panhandlers known as ‘lone wolves’ – that is they do not mix with others of their class.
1924		G. Henderson Keys to Crookdom 45: The lone wolf does not hobnob with other pickpockets and has no confidants.
1935		R. Chandler ‘Spanish Blood’ in Spanish Blood (1946) 12: He was a lone wolf, Pete. Sharp as a weasel.
1950		Goldin et al. DAUL 128/2: Lone wolf. 1. (Probably a journalistic creation, seldom heard in the underworld) A clever thief who operates alone. 2. (P) An active pederast who selects undercover perverts and maintains secrecy.
1953		‘Curt Cannon’ ‘Now Die In It’ in I Like ’Em Tough (1958) 51: ‘She friends with any of the girls who come in here?’ ‘I guess not [...] She was pretty much a lone wolf.’.
1972		B. Rodgers Queens’ Vernacular 155: A group of rapists is a wolf pack while one working single-o is a lone wolf.
1974		E.H. Hunt Undercover 146: ‘[W]hat do you think of the [Daniel] Ellsberg prosecution? [...] [D]o you think this guy is a lone wolf?’.

2. (US prison) one who does not enter a sexual relationship.

1958

Murtagh & Harris Cast the First Stone 34: Who wanted to be a crazy old lone wolf? Not me.