The Next Generation did a Jack the Ripper episode? That one escapes me. Do you recall what its title/season is?

I can't think of one.

But there was a TOS episode that involved Jack .... after a fashion (malevolent, non-corporeal, person-posessing, space-traveling entity that was responsible for a string of Ripper-esque murders on a planet that Enterprise was visiting and had apparently been behind the Jack case in London as well).