A topper in comic strip parlance is a small secondary strip seen along with a larger Sunday strip. In the 1920s and 1930s, leading cartoonists were given full pages in the Sunday comics sections, allowing them to add smaller strips and single-panel cartoons to their page.
Toppers usually were drawn by the same artist as the larger strip. These strips usually were positioned at the top of the page (hence their name), but they sometimes ran beneath the main strip.
Toppers were introduced by King Features Syndicate during the 1920s, enabling newspaper editors to claim more comic strips without adding more pages. The practice allowed newspapers to drop the topper and place another strip or an additional advertisement into the Sunday comics section. They also made it possible to reformat a strip from full-page size to tabloid size.
In 1904, Frederick Opper drew his And Her Name Was Maud, about the kicking mule Maud, into comic strips, books and animation, but on May 23, 1926, Opper positioned And Her Name Was Maud as the topper to his Happy Hooligan, and it ran along with Happy Hooligan until both strips came to a conclusion on October 14, 1932. On May 16, 1926, Harold Knerr began Dinglehoofer und His Dog, a topper to The Katzenjammer Kids, which ran until two years after his death. By 1936, to avoid any association with Hitler, the dog's name was changed from Adolph to Schnappsy (a.k.a. Schnapps). Knerr's strip was reformatted for reprints in Magic Comics in the early 1940s.
Billy DeBeck's topper for Barney Google was Parlor Bedroom and Sink, which evolved into Parlor Bedroom and Sink Starring Bunky and eventually was titled simply Bunky. In the mid-1930s, DeBeck added alongside Bunky a single-panel topper, Knee-Hi-Knoodles, depictions of kids' funny remarks (contributed by readers). Bunky spawned the catchphrase, "Youse is a viper, Fagin." A big fan of Bunky was pulp author Robert E. Howard, who liked to quote from the strip, as noted by his friend Tevis Clyde Smith:
His affection for Bunker Hill – "Youse is a viper, Fagin." Kept up with the strip, and retold it in a charming way. Liked to talk Brooklynese, and once entered a local dry goods store, and asked to see a shoitel.
Characters in toppers sometimes turned up in the main strip, such as Herby appearing in Smitty, and Kitty Higgins joining the cast of Moon Mullins. In a few cases, the topper introduced characters later developed into a successful Sunday page, as happened when Krazy Kat became a spin-off from The Family Upstairs and Roy Crane's Wash Tubbs appeared over J. R. Williams' Out Our Way with the Willets Sunday strip. The Wash Tubbs Sunday strip ran in that format from 1927 until 1933, when Crane launched Captain Easy as a Sunday page (featuring Wash Tubbs as a secondary character).
Gene Ahern's topper The Squirrel Cage, which ran above his Room and Board, is notable because of the repetitive use of the nonsensical question, '"Nov shmoz ka pop?", which was never translated yet became a national catchphrase. As a consequence, The Squirrel Cage is today better remembered than Room and Board, despite its 17-year run.
On at least one occasion, a character exited the topper and dropped down into the main strip. This happened on April 17, 1938, when an absent-minded character in the Rosie's Beau topper realized he was in the wrong place and climbed down into the first panel of Bringing Up Father, arriving in the living room of Maggie and Jiggs. During the 1940s, Snookums ran as the topper above Bringing Up Father. In the final episode of HBO's The Pacific (2010), Robert Leckie (James Badge Dale) is seen reading Snookums.
During its long run, Pete the Tramp had several topper strips, as detailed by comic strip historian Allan Holtz:
C. D. Russell's wonderful Pete the Tramp went through a trio of topper strips on its Sunday pages. The first, Pete's Pup, was a dog strip, sort of a canine counterpart to the Mutt and Jeff topper, Cicero's Cat. The next was The Topper Twins, my favorite because the name is an in-joke to the industry term "topper". For some reason, Russell alternatively called this strip The Tucker Twins. The last topper was Snorky... It started in 1935 and is believed to have run as late as 1939. Getting an end date on these later toppers can be a Herculean task, because fewer and fewer papers printed the toppers as the decade of the 1930s wore on. In fact, I have no examples of Snorky later than 1937 in my collection; the 1939 date is based on the strip's listing in the Editor & Publisher yearbooks.