Character is a moronic sort (7)
I believe the answer is:
omicron
'character' is the definition.
(omicron is a kind of character)
'moronic sort' is the wordplay.
'sort' indicates anagramming the letters.
'moronic' is an anagram of 'OMICRON'.
'is a' is the link.
(Other definitions for omicron that I've seen before include "Foreign letter -- I'm no roc (anag)" , "Greek vowel" , "Greek short 'o'" , "character in Sophocles" , "letter from Athens" .)