So many things can attain legendary status without there ever being proof of its existence: The Lock Ness Monster. Bigfoot. Chupacabra. Sarah Palin's intelligence. And Duke Nukem Forever.
The original Duke Nukem was released in 1991 as a simple side scroller, but it wasn't until the 1996 release, that our smart ass, wise cracking, womanizing anti-hero took the world by storm. The unique weapons, aliens, and, ahem, adult subject matter instantly became a classic, and a sequel, Duke Nukem Forever was promised..... in 1997.