Hyde's other self (6)
I believe the answer is:
jekyll
'hyde's other self' is the definition.
(I've seen this in another clue)
This is the entire clue.
(Other definitions for jekyll that I've seen before include "Doctor with an alter ego" , "The good personality (see 18)" , "Potato heap; immobilise (car)" , "The Strange Case of Dr . . . . . . and Mr Hyde" , "Famous novel 'Dr ...... and Mr Hyde'(6) ()" .)