Clark Kent (Superman in DC Comics) is also a character in the Marvel universe, where he's actually just a mild-mannered reporter and nothing more.
The first American woman to go to medical school was admitted as a joke. Geneva Medical School thought it was joke when Elizabeth Blackwell applied to attend 1847. She graduated in 1849, started her own practice, and opened an infirmary for the poor.
Bubble wrap was originally intended to be used as 3D wallpaper.