Jacks are around every corner

Astonishingly, Jack shows up everywhere — in music, in fairy tale, in slang and even in graffiti. Edwin Radford calls Jack, “The English language’s word of all work” (To Coin a Phrase).
Jack as equivalent to “Mac,” “Friend” and “fellow,” was known by 1889. The put-down, “Jack of all trades; master of none,” comes from this idea of Jack, the common man and may explain why the knave in a suit of playing cards is called the Jack.
Sometimes, Jack implies maleness, as in jack-rabbit and jack-ass (female asses are “jennies”). In 1823, jackass entered slang where it still designates a “fool.”
An old use of Jack is in Jackanapes (1450). This word refers to any male who thinks he is more important than he is. Jack the Lad is a smart-alecky young man. Not old, the phrase has been around only since the 1980s.
In other slang, jack-tar was British slang for “sailor” by 1781. Also nautical and British, Jack-Strop (1945) means an opinionated, pompous person. Jack, meaning money, entered U.S. slang in 1890. 
Although The Dictionary of Slang lists 84 slang uses of Jack, it’s found elsewhere. Jackknife has been in U.S. English since the early 1700s. Its origin is unknown. Brandy made from apple cider has been applejack since the early 1800s. 
Jackpot, today, refers to a big win in a lottery or at a slot machine. It’s actually poker jargon and comes from a type of draw poker where betting can’t start until someone is dealt a pair of Jacks.
To hijack (highjack) appeared in U.S, English about 1918. Thought to have originated in hobo slang, it’s no longer considered slang. It means to rob a vehicle. That vehicle is usually an airplane today, but originally it was a train. To jack, from hijack, is “to steal.” To jacklight is to hunt illegally at night.
Jack is a device for raising things. From that, we get jack up to describe that raising process.
Baseball fans know Jackie Robinson was the first Black to play major league baseball. But he isn’t the Jack Robinson in the saying, “Before you can say Jack Robinson.” No one knows who that Jack Robinson was, if, indeed, he ever existed. The saying originated in Britain in the late 1700s, but there was no well-known Jack Robinson back then. It seems to be a name snatched out of thin air.
Even if Jack Robinson is a mystery, we’ve plenty of other famous Jacks — Jack Dempsey of boxing fame, golfer Jack Nicklaus, assassinated U.S. President Jack Kennedy, author Jack London, comedian Jack Benny, and the infamous Jack the Ripper, to name a few.
And this was scribbled on a wall: “Jack and Jill are over the hill.”
Jack is usually considered a form of “John,” although some sources insist it’s incorrectly so-used. They say it’s from the French name “Jacques,” which is “James” in English. Jacques, itself, is likely from the Latin Jacobus (Jacob). However, Brewer’s Dictionary of Names says Jack is, “a pet form of John, evolving from Jankin, ‘little Jan.’”