"There is something here. Something terrible. I feel its presence.
Fear, anger, hatred... anger feeds the flame.
Oh, oh, there is evil here, monstrous, terrible evil! Consuming hunger!
Hatred of all that lives, hatred of women, a hunger that never dies!
It is strong, overpowering, an ancient terror!
It has a name: Beratis, Kesla, Redjac.
Devouring all life, all light! A hunger that will never die!
In other media (comic books, short stories, novels), the alien entity Redjac (once known as Jack the Ripper during Earth's Victorian age), returns to wreak havoc for several generations of the Enterprise crew. But as far as I can tell, no one has ever questioned the origins of Redjac.....
Redjac was a malevolent being comprised of pure energy, described as a highly cohesive electro-magnetic field . There was at least one other such alien race from 'Star Trek' that resembled Redjac's basic form - "The Lights of Zetar". And it's possible Redjac was an outcast from their society because of its depraved insanity. (As we saw in "The Lights Of Zetar", they weren't exactly saints themselves as a whole, but they were at the time fighting for their survival and driven to desperate measures.)
But since 'Doctor Who' will already be playing a small role in the history of Jack the Ripper, I thought to expand the show's participation in "The Redjac Chronicles" by looking to its history for the source of Redjac's ancestry.
There were several options for alien races which were pure energy in 'Doctor Who'. Among them would be the Helix Intelligence (which includes the Mandragora Helix) from "The Masque Of Mandragora" and from the spin-off series 'The Sara Jane Adventures' there was a species of energy beings who called themselves "The Ancient Lights". But I think the best option is that of the Xeraphin, featured in the Fifth Doctor adventure "Time-Flight".
Here are some excerpts from the description of the Xeraphin to be found in "The TARDIS Files", a 'Doctor Who' wiki:
The Xeraphin were highly psychic beings, able to wield psychokinetic energy, possess people in order to communicate, exert a hypnotic influence over people, and telepathically project components of their gestalt - such as people who have been absorbed into it - into other locations, even the interior of a TARDIS.
The power of the Xeraphin was controlled by two aspects, good and evil, of the same personality.
If Redjac was a member of the Xeraphin, it must have been a mutant - for it only had the one aspect. Redjac was pure evil.
The Xeraphin didn't become a single consciousness until after it was poisoned by radiation as it fled to Earth. I think Redjac had separated itself from the others long before the Vardon-Kosnax War, during which the Xeraphin were believed to have perished.
(Russell T. Davies believes that the Ancient Lights were related to the Mandragora Helix. I wrote about the possible connection of the Ancient Lights to the Lights of Zetar here. It could be that like all humanoids across the galaxy, all energy beings spread across space are basically related.)
Redjac either fled its own species before that war (possibly escaping incarceration for crimes it committed among them before they could execute it), or it was banished by its brethren because it was alien even to them as a mutant. It traveled the galaxy via one host after another, causing the same murderous mayhem which it would commit once it reached Earth.
One of those planets which was mentioned in the 'Star Trek' episode was not in the timeline for Redjac after it left Earth, so it's pozz'ble, just pozz'ble that Redjac struck there before arriving on the third rock from the Sun. There on Deneb II it was known as "Kesla" and Deneb II could have been the planet it terrorized before leaving for Earth. On another, unnamed, planet, it could be that Redjac so inflamed the emotion of fear among the populace that it may have triggered the rulers to launch their ultimate weapon - "The Doomsday Machine".
By 1887, Redjac found its way to Earth. It couldn't be any earlier in the timeline of Earth Prime-Time because there really isn't any record of serial killer attacks of such magnitude ("Pop! Pop!") before then. And the first suspected killing by Jack, although not considered canonical, was on December 26, 1887. Redjac would have needed to feed by that time had it arrived much earlier.
How did Redjac get to Earth?
Simple. It hitched a ride via a humanoid host.
As of now, there is no recorded presence of the Doctor on Earth Prime-Time between 1885 (when he encountered H. G. Wells in "Timelash") and late 1888, when he arrived in London after the official Ripper murders ended. (Thanks to Vastra in "A Good Man Goes To War".)
(The Doctor - his seventh incarnation, principally - did battle with Jack the Ripper on several occasions actually. But that would be the Doctor to be found in novels, comic books, and audio-plays; and thus having nothing to do with the TV Universe. But if you're interested in that topic, perhaps as an ardent overall crossoverist, then I'd like to recommend a blog for you - "Who Etc.", in which a Whovian named Thomas tackled that topic in a seven part essay over a three month period, beginning in June. He's also got one of the best blog headers I've ever seen!)
Once on Earth, there's a way by which Redjac could have arrived in London by December 26, 1887, ready to feed. Via a host that is humanoid, but not altogether human.....
With Santa Claus, on the night before Christmas.....
Look out, Miss! That ain't Father Christmas! It's the Ripper!
Ho Ho Ho, ho's!