Facial expression of Greek character, last character in line-up? (4)
I believe the answer is:
phiz
'facial expression' is the definition.
(I've seen this before)
'greek character last character in line-up?' is the wordplay.
'greek character' becomes 'phi' (letter from the Greek alphabet**).
'last character in line-up?' becomes 'z' (last letter of the alphabet).
'phi'+'z'='PHIZ'
'of' acts as a link.
(Other definitions for phiz that I've seen before include "Facial expression" , "Dickens's illustrator" , "former illustrator" , "mug" , "Dial" .)