Characters in Aristophanes perhaps finding most essential part (5,3,5)
I believe the answer is:
alpha and omega
This clue is a double definition.
'characters in aristophanes perhaps' is the first definition.
(Greek letters)
'most essential part' is the second definition.
(alpha and omega can mean something's essence)
'finding' is the link.
(Other definitions for alpha and omega that I've seen before include "identifying with God?" , "Two extremists literally" , "Extremist characters in Athens" , "used to describe the deity" , "The beginning and end (of the matter)" .)