For example:
* Jack Nicholson: A famous actor. We don't know his religious beliefs as he hasn't publicly discussed them.
* Jack Black: A famous actor and musician. He has publicly stated that he is Jewish.
* Jack Kerouac: A famous writer. He was raised Catholic, but later became interested in Buddhism.
* Jack Sparrow: A fictional character from the "Pirates of the Caribbean" series. His religion is never mentioned in the films.
Please tell me which "Jack" you are interested in, and I can give you a more accurate answer.