I actually read a "Jack the Ripper" theory once that speculated the Ripper was none other than Joseph Merrick, AKA The Elephant Man. It seems he was housed in the London Hospital during the Ripper murders and it was close enough to the crime scenes that he could sneak out at night and commit the murders!
By the way, I have no idea if any of this (time, location, etc.) is remotely accurate.
Of course, EVERYBODY knows the Ripper was actually a bit of ancient evil gas that looked like this:
... and traveled around the galaxy murdering women until defeated in the Star Trek
episode "Wolf in the Fold".
I mean, come on
Rumor is he was also spotted as a human frog using the alias "Fergus Finglehoff" on Bewitched
and as a patient of Dr. Bob Hartley on The Bob Newhart Show