Jack shows up in stories too, Jack and beanstalk being the most well known Jack story, but there are others.. in the television production of The Story of English, Jack (and jack stories) was one word that had a large part of an episode devoted to it.

and a jack of all trades.. (a general handyman/person) is a well know 'jack'.

jack shows up in lots of idioms. you can high tail out of a place, but if you take an others car, or vehicle, you highjack it.

i am sure there are other jack words and idioms.