Greek character in some gangs (5)
I believe the answer is:
omega
'greek character' is the definition.
(letter from the Greek alphabet)
'in some gangs' is the wordplay.
'in' says the answer is hidden in the clue.
'OMEGA' can be found hidden inside 'some gangs'.
(Other definitions for omega that I've seen before include "Last (Gk. letter)" , "Traditional story" , "completes a series" , "Ultimate letter" , "end of series" .)