Superman is the only Superhero who IS the Superhero, and the regular person is the alter ego.
Bruce Wayne's alter ego is Batman, Peter Parker's alter ego is Spiderman, Tony Stark's alter ego is Iron Man...but Clark Kent is Superman's alter ego.
There was something mentioned like this in Kill Bill Vol. 2. Bill was talking to the Bride and gave a similar speech about superhero mythology. Peter Parker has to put on a costume to become Spiderman. Superman wakes up as Superman. His costume is Clark Kent and that is how he views us.