My younger granddaughter showed me her new toy of a box, from which a doll popped out when she opened the lid. I asked her what the name of toy is, she said she does not know. Well, she is just two and a half. But her elder sister did. It is a jack-in-the-box. 

Besides jack-in-the-box, there are also several usages related to jack. As far as I know, there are:

jack-of-all-trade: A person who can do many different types of work.

jack-o-lantern: a hollowed pumpkin with a face outside and a candle inside.

jackhammer: a large, powerful drill

jackfruit: a large tropical fruit like pineapple 

jackdaw: a kind of crow

.....

PS But why is Jack?