Green’s Dictionary of Slang

nobody, a nameless person.

[1849		Dickens David Copperfield 17: ‘Take care, if you please. Somebody’s sharp. [...] ‘Only Brooks of Sheffield,’ said Mr Murdstone].
1887		Referee 31 July in Ware (1909) 49/2: Never mind; I hear that Smith, the champion pugilist of the universe and all England, is going to find out who that there Brooks of Sheffield is who boasts that he knocked Smith out in a private glove fight.
1908		Sheffield Indep. 5 Oct. 5/2: ‘Brooks of Sheffield’ a symbol — Mr J. Cummings Walters [...] in a flippantly humorous way discussed the great Brooks mystery.