Russian reformer disheartened monk disturbed by even his reforming (9)
I believe the answer is:
menshevik
'russian reformer' is the definition.
(type of Russian socialist)
'disheartened monk disturbed by even his reforming' is the wordplay.
'disheartened' suggests removing the centre (the middle or heart is removed).
'disturbed by' indicates putting letters inside (inserted letters disturb or break up the word).
'reforming' indicates an anagram.
'monk' with its centre removed is 'mk'.
'even'+'his'='evenhis'
'evenhis' with letters rearranged gives 'enshevi'.
'mk' placed around 'enshevi' is 'MENSHEVIK'.
(Another definition for menshevik that I've seen is " Moderate Russian".)