The earliest existing Keystone Kops movie is April 1913's "The Bangville Police." The Kops made their first tentative introduction a year before in "Hoffmeyer's Legacy," but because it's a lost film, movie historians don't consider the movie as their introduction to cinema. Even in "The Bangville Police," the hapless group of pratfallers weren't identified as the Keystone Kops (or known as Cops in the early going). They appear as a deputized group of clumsy chumps responding to farm girl Mabel Normand's plea over the phone to police chief Fred Mace to save her from a couple of burglars roaming about.
The Keystone Kops, an idea originating from Keystone Studio's main comedian Hank Mann's suggestion, appeared in 12 movies, mostly in support roles to the studio's later bigger stars, such as Charlie Chaplin and Fatty Arbuckle.
In "The Bangville Police," Fred Mace takes center stage as the leader of the Kops. Once reaching stardom as the Keystone police chief, Mace became itchy and left the studio for other acting and film producing endeavors. However, none panned out and he returned to Keystone in 1917, only to get vastly diminished roles. He bemoaned his fate, and in a New York City hotel room, Mace died of a massive stroke on February 21, 1917, at age 39.
In their screen lifetime, Keystone Kops consisted of a revolving troupe of actors supported by some mainstays, including Edgar Kennedy. He had quite a career as a well-known character actor later in his life, appearing with the Marx Brothers and Laurel & Hardy among others.
