The Fortress of Solitude originally appeared in Superman #58 in 1949. It was a direct "borrow" from the fictional character Doc Savage who's Fortress of Solitude made its first appearance in 1932. Superman and Batman took many elements of Doc Savage, a moral hero who is a great scientist, great detective, and physically trained from birth to be the ultimate physical speciman.
Doc Savage originally appeared in the pulps of the 30s and 40s but gained modern fame when Bantam Books republished his adventures in paperback form 1964 through 1990. I would suggest anyone who loves comics read at least the first book, The Man of Bronze (sound familar with just a little change for a later hero?) It is a true comic book adventure in novel form. His five friends and assistants could be seen as a prototype for later superhero teams. It may come as an odd form of irony that both DC, Marvel, and other publishers have published Doc Savage comics over the years.
There was a disastrous movie made in the mid-70s that almost damaged the character irreparably but there has been discussion of a new movie for years with various big name stars attached. We can only hope that one day we'll see hin on the big screen protrayed properly.
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