Superman's alter ego (4)
I believe the answer is:
kent
'superman's alter ego' is the definition.
(I've seen this in another clue)
This is the entire clue.
(Other definitions for kent that I've seen before include "Lear's faithful Earl" , "Canterbury's county" , "Home county" , "Part of 1 25 [KING LEAR]" , "Garden of England - Superman's family name" .)