Answer the question at the end by quoting:

The Joker is a fictional supervillain created by Bill Finger, Bob Kane, and Jerry Robinson who first appeared in the debut issue of the comic book Batman (April 25, 1940), published by DC Comics. Credit for the Joker's creation is disputed; Kane and Robinson claimed responsibility for the Joker's design, while acknowledging Finger's writing contribution. Although the Joker was planned to be killed off during his initial appearance, he was spared by editorial intervention, allowing the character to endure as the archenemy of the superhero Batman. In his comic book appearances, the Joker is portrayed as a criminal mastermind.
The Joker debuted in Batman #1 (Spring 1940) as the eponymous character's first villain, shortly after Batman's debut in Detective Comics #27 (May 1939). The Joker initially appeared as a remorseless serial killer, modeled after a joker playing card with a mirthless grin, who killed his victims with "Joker venom": a toxin which left their faces smiling grotesquely. The character was intended to be killed in his second appearance in Batman #1, after being stabbed in the heart. Finger wanted the Joker to die because of his concern that recurring villains would make Batman appear inept, but was overruled by then-editor Whitney Ellsworth; a hastily drawn panel, indicating that the Joker was still alive, was added to the comic. The Joker went on to appear in nine of Batman's first twelve issues. The character's regular appearances quickly defined him as the archenemy of the dynamic duo, Batman and Robin; he killed dozens of people, and even derailed a train. By issue #13, Kane's work on the syndicated Batman newspaper strip left him little time for the comic book; artist Dick Sprang assumed his duties, and editor Jack Schiff collaborated with Finger on stories. Around the same time, DC Comics found it easier to market its stories to children without the more mature pulp elements that had originated many superhero comics. During this period, the first changes in the Joker began to appear, portraying him more as a prankster than threat; when he kidnaps Robin, Batman pays the ransom by check, meaning that the Joker cannot cash it without being arrested. Comic book writer Mark Waid suggests that the 1942 story "The Joker Walks the Last Mile" was the beginning point for the character's transformation into a more goofy incarnation, a period that Grant Morrison considered lasted the following thirty years. The 1942 cover of Detective Comics #69, known as "Double Guns" (with the Joker emerging from a genie lamp, aiming two guns at Batman and Robin), is considered one of the greatest superhero comic covers of the Golden Age and is the only image of the character using traditional guns. Robinson said that other contemporary villains used guns, and the creative team wanted the Joker--as Batman's adversary--to be more resourceful.

How did the Joker become the Joker?

IN: Joseph Frank "Buster" Keaton (October 4, 1895 - February 1, 1966) was an American actor, comedian, film director, producer, screenwriter, and stunt performer. He was best known for his silent films, in which his trademark was physical comedy with a consistently stoic, deadpan expression, earning him the nickname "The Great Stone Face". Critic Roger Ebert wrote of Keaton's "extraordinary period from 1920 to 1929, [when] he worked without interruption on a series of films that make him, arguably, the greatest actor-director in the history of the movies". His career declined afterward with a dispiriting loss of his artistic independence when he was hired by Metro-Goldwyn-Mayer and he descended into alcoholism, ruining his family life.

Keaton's personal life had stabilized with his 1940 marriage, and now he was taking life a little easier, abandoning Columbia for the less strenuous field of feature films. Throughout the 1940s, Keaton played character roles in both "A" and "B" features. He made his last starring feature El Moderno Barba Azul (1946) in Mexico; the film was a low budget production, and it may not have been seen in the United States until its release on VHS in the 1980s, under the title Boom in the Moon. Critics rediscovered Keaton in 1949 and producers occasionally hired him for bigger "prestige" pictures. He had cameos in such films as In the Good Old Summertime (1949), Sunset Boulevard (1950), and Around the World in 80 Days (1956). In In The Good Old Summertime, Keaton personally directed the stars Judy Garland and Van Johnson in their first scene together where they bump into each other on the street. Keaton invented comedy bits where Johnson keeps trying to apologize to a seething Garland, but winds up messing up her hairdo and tearing her dress. Keaton also had a cameo as Jimmy, appearing near the end of the film It's a Mad, Mad, Mad, Mad World (1963). Jimmy assists Spencer Tracy's character, Captain C. G. Culpepper, by readying Culpepper's ultimately-unused boat for his abortive escape. (The restored version of that film, released in 2013, contains a restored scene where Jimmy and Culpeper talk on the telephone. Lost after the comedy epic's "roadshow" exhibition, the audio of that scene was discovered, and combined with still pictures to recreate the scene.) Keaton was given more screen time in A Funny Thing Happened on the Way to the Forum (1966). The appearance, since it was released after his death, was his posthumous swansong. Keaton also appeared in a comedy routine about two inept stage musicians in Charlie Chaplin's Limelight (1952), recalling the vaudeville of The Playhouse. With the exception of Seeing Stars, a minor publicity film produced in 1922, Limelight was the only time in which the two would ever appear together on film. In 1949, comedian Ed Wynn invited Keaton to appear on his CBS Television comedy-variety show, The Ed Wynn Show, which was televised live on the West Coast. Kinescopes were made for distribution of the programs to other parts of the country since there was no transcontinental coaxial cable until September 1951.

Great. What else?

OUT:
Sunset Boulevard (1950),