1660s, earlier Will with the wisp (c. 1600), from the masc. proper name Will + wisp "bundle of hay or straw used as a torch." Compare Jack-o'-lantern.

"person or thing that people hope will be very successful in the near future," 1911, originally in U.S. sporting use in reference to the quest for a white man capable of beating champion pugilist Jack Johnson.

also david, "crane-like structure on the side or stern of a vessel for suspending or lowering a boat," late 14c., daviot, apparently a use of the masc. proper name David on the pattern of applying common Christian names to useful devices (compare jack, jenny, jimmy).

1530s, typical name for an English woman of the lower class, hence "girl, lass, sweetheart," sometimes also "strumpet," from the pet form of Isabel. Often paired with Tom, as Jill was with Jack. Colloquial St. Tibb's Eve (1785) was the evening of the last day, the Day of Judgment, hence "never."

"a buffoon; a zany; a jack-pudding" [Johnson], "One whose business it is to make sport for others by jokes and ridiculous posturing" [Century Dictionary], according to OED, in early use properly a mountebank's assistant, 1670s, from merry + masc. proper name Andrew, but there is no certain identification with an individual, and the name here may be generic.

by 1926, "mediocre prizefighter," of unknown origin, credited to U.S. sportswriter and Variety magazine staffer Jack "Con" Conway (1898-1928), who might at least have popularized it. Non-boxing sense of "average person" is from Joe Palooka, hero of Ham Fisher's boxing-themed comic strip, which debuted in 1930.