Clark Kent's glasses

Clark Kent's glasses are the key to his disguise. Since Superman doesn't wear a mask, he wears glasses so that people wouldn't recognize that he and Superman are the same person.

History
Clark Kent first put on the fake glasses to fool his High School football coach into thinking his vision was impaired, so that he wouldn't be recruited to play football. But within a short period, he uses the glasses to create an alternate identity. When his mother sews his Super-Suit, he dons it, and he becomes known as Superboy, and while out-of-costume, he resumes his role as Clark Kent, under the glasses he wears, while slouching and acting like a bumbling clutch. It was so much more than just the glasses that made him appear that he was a different person. His bumbling personality and his tendency to constantly be late made it seem impossible that Clark Kent and Superboy (later Superman) were the same person.