Coming back, sit beside a Greek author (5)
I believe the answer is:
aesop
'greek author' is the definition.
(I've seen this before)
'coming back sit beside a' is the wordplay.
'coming back' says the letters should be written backwards.
'sit' becomes 'pose' (as in sitting for a painter).
'beside' says to put letters next to each other (I've seen this in other clues).
'pose' reversed gives 'esop'.
'esop' after 'a' is 'AESOP'.
(Other definitions for aesop that I've seen before include "Greek teller of animal tales with a moral" , "Greek author, famous for his fables" , "Fabulous man" , "he wrote in Greek" , "his writings were fabulous" .)