Government appointee that's a Russian infiltrator (4)
I believe the answer is:
tsar
'government appointee' is the definition.
'that's a russian infiltrator' is the wordplay.
'infiltrator' says the answer is hidden in the clue (the answer has infiltrated the clue ).
'TSAR' is hidden in the letters of 'thats a russian'.
(Other definitions for tsar that I've seen before include "Male monarch" , "Nicholas II was the last" , "Word derived from Caesar, used by European rulers since 1547" , "Title of Russian emperor" , "Rats to the Russian emperor" .)