What are the odds that two comics come out on the same day with the exact same name in two different countries? I'm no mathematician so I'm not going to try and calculate them, but I will say they are pretty slim.
That is exactly what happened on March 12, 1951 in the US and England. In America, Hank Ketcham released his Dennis the Menace comic strip. It is still around today. In England, issue No. 452 of "The Beano" comic strip came out and introduced a character named Dennis the Menace. The character went on to become cartoonist David Law's most famous character.
Neither author knew about the other's plans beforehand. The characters do not look that much alike but both have a tendency for mischief. No lawsuits were filed and the characters kept their names. In 1993, a movie version of the American Dennis the Menace came out, and when it was marketed in Britain, it was just called "Dennis" to avoid any copyright infringement.