When will Superman become public domain? Superman was created back in 1933, so he will turn 100 in just 19 more years.
		
		
	 
Not sure how it works, don't they go by day of first publication? If so 
Superman 1938, he has to get in line behind (just to name a few favorites

) :
1887 - Sherlock Holmes
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1897 - Dracula 
1897 - The Invisible Man
1898 - The War of the Worlds
1898 - The Black Corsair 
1900 - Dorothy Gale, Wizard of Oz
1903 - The Scarlet Pimpernel 
1904 - Rima Green Mansions
1909 - The Phantom of the Opera 
1911 - Fantômas
1912 - Tarzan  
1912 - John Carter 
1915 - Doctor Syn
1916 - Judex 
1919 - Zorro 
1926 - The Bat 
1928 - Solomon Kane 
1928 - Mickey Mouse 
1929 - Buck Rogers
1929 - Popeye 
1930 - The Shadow 
1930 - The Bat Whispers 
1931 - Dick Tracy
1932 - Conan 
1933 - The Lone Ranger 
1933 - Doc Savage 
1933 - The Spider 
1934 - Flash Gordon 
1934 - Mandrake the Magician
1935 - Doctor Occult also  Siegel &  Shuster 
1936 - The Green Hornet 
1936  - The Phantom 
1936 - Ka-Zar 
1937 - Prince Valiant
1937 - The Hobbit, Gandalf
1937 - Sheena
1938 - Superman Action Comics #1
Although many of those seem to have lapsed, maybe they weren't defended? Or it depends how powerful their lawyers were

. 
The likes of Mickey Mouse and Superman lapsing will probably force laws changed, if they haven't already.