mid-15c., "a monkey," also "an impertinent, conceited fellow, an absurd fop," a general term of reproach (in mid-15c. especially a contemptuous nickname for William de la Pole, Duke of Suffolk), of unknown origin. Apparently from Jack of Naples, but whether this is some specific personification of Jack (which is attested from 16c. as "saucy or impertinent fellow") or folk etymology of jack (n.) + ape (n.) is unknown. See extensive note in OED. Century Dictionary suggests "orig., it is supposed, a man who exhibited performing apes." Farmer and Henley ("Slang and Its Analogues") say "originally, no doubt, a gaudy-suited and performing ape." Its fem. counterpart is Jane-of-apes (Massinger) "a pert, forward girl."

1540s, "the common daw," a type of small European crow (Corvus monedula), "which frequents church towers, old buildings, etc.; noted for its loquacity and thievish propensities" [OED]. See jack (n.) + daw.

In modern times, parrots are almost the only birds that have the gift of speech, though connoisseurs are not ignorant that starlings and jackdaws have good abilities in that way, when properly educated. ["Chambers' Home Book and Pocket Miscellany," 1853]

In U.S. sometimes applied to a species of grackle.

also jack-pot, "big prize," 1944, from slot machine sense (1932), from now-obsolete poker sense (1881) in reference to antes that begin when no player has a pair of jacks or better; from jack (n.) in the card-playing sense + pot (n.1). Earlier, in criminal slang, it meant "trouble," especially "an arrest" (1902).

The regular Draw-Poker game is usually varied by occasional Jack-Pots, which are played once in so many deals, or when all have refused to play, or when the player deals who holds the buck, a marker placed in the pool with every jack-pot. In a jack-pot each player puts up an equal stake and receives a hand. The pot must then be opened by a player holding a hand of the value of a pair of knaves (jacks) or better. If no player holds so valuable a hand the deal passes and each player adds a small sum to the pot or pool. When the pot is opened the opener does so by putting up any sum he chooses, within the limit, and his companions must pay in the same amount or "drop." They also possess the right to raise the opener. The new cards called for are then dealt and the opener starts the betting, the play proceeding as in the regular game. [Encyclopaedia Britannica, 11th ed., 1911, "Poker." The article notes "Jack-Pots were introduced about 1870."]

To hit the jackpot "be very successful" is from 1938.