What is a 'Jack' (as in Jack, Queen, King') ? When was it so designated?

In Charles Dicken's Great Expectations, published in 1861, when Pip, the hero, plays cards with his friend Estella, the narrative states :

“He calls the knaves Jacks, this boy!” said Estella with disdain, before our first game was out. “And what coarse hands he has! And what thick boots!”

So what does a 'Jack' represent and was this the first time that it had been so described in English literature ?

OED has

24. Cards. Originally in the game of all fours: (a name for) the lowest court card of the suit which is trumps, which earns the player who takes it a point; now rare. Later gen. (originally colloquial): the lowest court card of any suit in a pack of cards, ranking below the queen and above the ten, and bearing a representation of a soldier or a pageboy; = knave

In the later more general sense, superseding knave as the usual term from the late 19th cent. Acceptance of Jack as standard was possibly driven by the introduction of corner index letters and numbers on playing cards in the late 19th cent., J thus being distinct from K (for King).

The earliest citation OED has for Jack is from Charles Cotton's The Compleat Gamester of 1674:

This game...is called All-fours from Highest, Lowest, Jack, and Game, which is the Set as some play it.
He that wins Jack wins one [point] also.

OED's conjecture about the "late nineteenth century" is given the lie by one of its own citations, although the importation of an Americanism might be what caused Estella's disdain.

1830 Adams Sentinel (Gettysburg, Pa.) 22 June 2/2 I'll bet any man ten dollars I can cut the Jack of hearts at the first attempt.