Jack the Ripper was secretly Jonathan "John" Kelsey, a London doctor with a practice near Whitechapel. He was assisted (in doctoring, not in ripping) by Penny Bower, a young woman who he saved from a life of prostitution. Kelsey's family suspected he may be the Ripper, and were working to get him quietly privately committed (instead of publicly arrested).
In 1888, while the Ripper murders were in progress, time-traveling vampires Mary, Queen of Blood and Andrew Bennett arrived in Whitechapel from the future. Mary had traveled to the past to prevent the birth of Allen Barr, a cancer researcher who discovered a cure for cancer that also changed the blood of the cancer survivors so it was poisonous to vampires. Bennett had followed Mary to stop her, although he didn't know what her plan was.
Shortly after arrival, Bennett was mistaken for Jack the Ripper. Fleeing, but weak from not feeding, he collapsed and was taken in by Dr. Kelsey and Miss Bower. Dr. Kelsey gave Bennett a transfusion of his own blood. Bennett assisted Kelsey with his medical work. When a newspaper arrived with a sketch of Bennett's face under the headline "Ripper Strikes Again!", Kelsey made plans to prove to Scotland Yard that Bennett was not the Ripper.
Bennett recalled an article he read about Allen Barr, the inventor of the cancer serum, who was described as "the son of a Soho mother who, in her younger days, narrowly escaped becoming the victim of Jack the Ripper." He then deduced that Mary's plan was to kill Barr's mother, preventing Barr's birth.
Bennett convinced Bower to help him find Mary. They did, at a place called "Taylor and Holmes". Bower's sister, Lacey, was apparently dead on the ground, a victim of Mary (posing as the Ripper). Bennett confronted Mary, but, as she tried to make her escape, Kelsey grabbed her arm, revealing himself as the Ripper. Mary managed to escape, and Kelsey accidentally stabbed himself to death struggling with Bennett (as he turned into a bat).
Two bobbies appeared, one named Officer Joseph Allen Barr, presumably Penny Bower's future husband and parent (with Penny) of Allen Barr. Mary used her magic to travel forward in time, taking Bennett along with her.
What happened next is unclear, but Dr. Kelsey was not publicly named as Jack the Ripper, and his death was not reported to his family, who believed he fled London to avoid being committed. A month later, his body was found in the River Thames.
It is believed that the man who earned the nickname "Jack the Ripper" was actually possessed by a demon named Calibraxis. Calibraxis also possessed an important member of the British royal family in the 1990s. 
Madame Xanadu visits Whitechapel during the Ripper killings and the Phantom Stranger eventually reveals why he must be allowed to kill. The Ripper's last victim, Mary Kelly, would have sired a son by Jason Blood who would have grown into a despot the likes humanity could not imagine.
The Ripper ran afoul of the Stranger and, terrified, fell into an open sewer to be, presumably, eaten by the rats.
It has been theorized that Vandal Savage may have either been Jack the Ripper or at the very least a close associate. Savage has claimed to have been many notable historical figures throughout his life, and his own testimony cannot always be considered reliable.  Another claimant to the role of Jack the Ripper is the delusional super-villain Red Jack. Red Jack is an adversary of the Doom Patrol.
A version of Jack the Ripper appears in the Elseworlds story Batman: Gotham by Gaslight. In this reality, Jack the Ripper is actually Jacob Packer, a close friend of Bruce Wayne. Wayne is temporarily imprisoned for the Ripper's crimes, but later escapes and captures the real Jack the Ripper. Jacob was ultimately killed by James Gordon in self-defense when the killer tried to kill Bruce.
The entire British Royal family was wiped out in an explosion in the 19th century, except the Duke of Clarence, who is confined to a wheelchair, and a distant American cousin, Jack Planters, who becomes King. Planters is Jack the Ripper and under his rule the British Empire becomes steadily more misogynistic.
Jack was killed when the catatonic Duke of Clarence tackle him in his wheelchair sending Jack to fell on a dense bundle of stakes, impaling him to death.
- The real Jack the Ripper has been seen in various works of fiction, including those of DC Comics. However, he has not been depicted in a consistent manner - different writers use the character as they see fit, with little continuity between them.
- This character is a fictional representation of Jack the Ripper, a real person. More information on this person can be found at Wikipedia.org.
- Red Jack, a supernatural entity who fought the Doom Patrol claimed that he was Jack the Ripper. Then again, he was also completely convinced that he had been God as well... not a very reliable character altogether, really.
- 11 Appearances of Jack the Ripper (New Earth)
- 3 Images featuring Jack the Ripper (New Earth)
- Quotations by or about Jack the Ripper (New Earth)
- Character Gallery: Jack the Ripper (New Earth)
- Jack the Ripper at dccomics.com
- Jack the Ripper at Wikipedia.org
- Jack the Ripper entry at Cosmic Teams
- wikipedia:Jack the Ripper at Wikipedia