E.g. James Stuart, an indulger in make-believe? (9)
I believe the answer is:
pretender
'indulger in make-believe?' is the definition.
(someone who pretends)
I cannot understand how the remainder of the clue works.
(Other definitions for pretender that I've seen before include "fake" , "Claimant to a throne, usually without just title" , "One claiming a title" , "Claimant, like Bonnie Prince Charlie" , "One who claims a title or position" .)