Wilhelm Busch drew the original Max und Moritz strip in the 1860s. It consisted of 7 adventures of two louts who, in the end, meet their well-deserved fate, deplored by no one. Max and Moritz became the best-known characters Busch designed in a very rich lifetime's production.
the nasty originals
In 1897, they were recreated by Rudolph Dirks as Hans and Fritz, the Katzenjammer Kids, for the New York Journal's Sunday Supplement "The American Humorist". Dirks changed their characters from rotten no-goods to two twins battling authority, in whatever form it came. They became immensely popular. In 1903 they even made it to a stage production (Little Orphan Annie took a lot longer to achieve that fame.)
Half a century later, Harvey Kurtzman and Bill Elder, no great lovers of authority themselves, did a wonderful spoof for MAD Magazine. The title was changed to "the Katchandhammer Kids" and their names to Hans und Freetz, no doubt for copyright reasons. The characters went back to pretty nasty, much more like the originals. They had at least one other appearance in MAD.
Now, after a century and a half, these powerful pests are still at it! As King Features Syndicate proudly remarks, this makes it the oldest syndicated comic strip around. It is now drawn by Hy Eisman. Meanwhile, MGM made a very popular cartoon series starring them, and it seems they even appeared on a U.S. Postal Service stamp: Help stamp out Hans and Fritz!