Controversial diarist: Mister X? (8)
I believe the answer is:
crossman
'controversial diarist' is the definition.
(Richard Crossman, politician and diarist)
'mister x?' is the wordplay.
I cannot really understand how this works, but
'x?' could be 'cross' (I've seen this before) and 'cross' is found within the answer.
The remaining letters 'man' is a valid word which might be clued in a way I don't see.
This may be the basis of the clue (or it may be nonsense).
Can you help me to learn more?
(Other definitions for crossman that I've seen before include "Political diarist" , "who wrote political diaries?" .)