Jack the Ripper (Batman: Gotham By Gaslight)

"I fooled all London. And I could fool them anywhere, even in Gotham City, if that's where I chose to appear."

- Jack the Ripper, in a letter "from hell"

"Wayne promised this world's fair would be a paradise of cleanliness and light. But what does a light in the darkness do? It draws flies. Vile, unclean. Like YOU. But for every one of you I eradicate, two more arrive. I promised the people of Gotham to clean the scum off the streets. Thieves, murderers, confidence men, immigrants, illiterates, anarchists. This city seems to spawn them. But it's WHORES, you painted whores, that are the worst. All rosy cheeked, soft, and round on the outside. But on the inside...(...) Yes, sadly your death will exonerate Wayne. But it will be worth it. Your blood shall christen this fair, woman. Your corruption and decay will spill down over this carnival as a warning to all your kind. Shall we begin? This may take quite some time..."

- Jack the Ripper to Selina Kyle after drugging her and revealing his true identity, right before trying to kill her

Jack the Ripper is the main antagonist of the DC Elseworlds comic book story Batman: Gotham by Gaslight, and it's animated movie adaptation. He is a fictionalized version of the infamous real life serial killer of the same name, though his true identity differs between the comic and movie versions. In both however, he comes to Gotham City to continue his murders of prostitutes.

In the Comic
Jack first appears in Gotham hunting women, apparently to stop "her" from laughing at him, as he finds this unidentified woman's laughter unbearable, and something that he can only silence by killing various prostitutes. Soon, Batman happens upon him and begins trying to stop him. Later, evidence is planted in Bruce Wayne's home that pins the Jack the Ripper murders on him.

Desperate to discover the killer's identity, Bruce Wayne pores over all of the evidence in his cell, but finds nothing that the police who Jack has already fooled did not already find. Just when it looks like Bruce is about to give up, he realizes that the symbol on a knife used by Jack is identical to a symbol used by his late father and his old Civil War buddies. From this, Bruce realizes who the killer is. After escaping from prison and becoming Batman once more, he confronts and unmasks the killer as his life-long friend Jacob Parker. It comes to light that the man who had been an old friend of Bruce Wayne's family had in fact had his parents killed in vengeance for Martha rebuffing his romantic feelings for and even cruelly laughing in his face. However, the killing of Martha Wayne and her husband brought Jacob Parker no peace, as he continued to hear her "laughing" at him whenever he looked at a woman, and so resolved to kill as many as he could both in England and in Gotham to "silence" it. Once Bruce Wayne came back into his life, Jacob knew he had to frame him to both complete his revenge against Martha Wayne by eliminating her son, and also get his costumed alter-ego off his trail.

His tale complete, Jacob Parker is at Batman's mercy. The Dark Knight strongly considers killing him, but decides not to, and Jacob Parker is then shot dead by James Gordon and the police when they arrive in the graveyard he and Batman were, ending the threat of Jack the Ripper for good.

In the Movie
In the movie, Jack is first introduced violently murdering prostitute Pamella "Ivy" Isley. Later, he attempts to kill Selina Kyle when she goes after him with the intent of stopping him. However, he proves a more skilled fighter than she thought, nearly killing her before Batman arrives to engage him. Jack fights relatively evenly with Batman for a time, but soon gains the upper hand before Batman pulls a trap door lever, sending him plummeting.

Later, Jack murders Sister Leslie, and shortly after that confronts Doctor Hugo Strange in Arkham Asylum, killing him as well before having a prolonged chase with Batman that takes them to an air zeppelin. The two again fight to a standstill, the fight ending when the zeppelin gets shot down. The police pursue Batman, and Jack disappears. Shortly after, a woman who tried to extort Bruce Wayne for money to keep silent about her having seen him in the Church Graveyard when Sister Leslie was killed, is found dead. This time, Bruce Wayne appears the guilty party, and is arrested. Tried for murder, he's incarcerated, only to then escape from prison after Selina decides to tell Gordon he's Batman so that he'll be released (as Batman has an alibi for the Ripper murders).

Unfortunately, it comes to light that, in fact, James Gordon himself is Jack the Ripper, having gone mad after the Civil War and devolved into a deranged, misogynistic zealot out to purge Gotham City of all those he views as unfit to live, including not just "harlots" and prostitutes but also common criminals and even illiterates and immigrants. Injecting Selina Kyle with a sedative, he tries to kill her in her drugged state, but Batman (having discovered on his own that James is the Ripper), follows him to the Gotham World's Fair and engages him once more. This time, Batman emerges the victor, handcuffing Gordon to a rail with his own cuffs. Refusing to let himself be taken alive, Gordon allows himself to be incinerated, ending the threat of Jack the Ripper.

Trivia

 * Though Jack's true identity of Jacob Parker is not his identity in the film, Bruce's lawyer in the animated film does greatly resemble Parker (who also represented him as a lawyer in the comic proper).
 * The movie version's background as a champion boxer brings to mind Professor Moriarty as he was in Sherlock Holmes: A Game of Shadows, who likewise was a former boxing champion (thus explaining his combat skills). Given the deliberate similarities between Gaslight Batman and Sherlock Holmes, this similarity may not be coincidental.
 * Ironically, the movie version's portrayal of James Gordon as a murderous psychopath bereft of any honor or compassion, is highly reminiscent of James Gordon's son in the comic books, who has his father's name.
 * In another ironic twist, his murdering Sister Leslie (the movie's equivalent to Doctor Leslie Tompkins), given that the two are romantically involved in the show Gotham.