Leader of USSR left in dishonour (6)
I believe the answer is:
stalin
'leader of ussr' is the definition.
'Stalin' can be an answer for 'leader' (Stalin is an example). I am not certain of the 'of ussr' bit.
'left in dishonour' is the wordplay.
'left' becomes 'l' (common abbreviation).
'in' is an insertion indicator.
'dishonour' becomes 'stain' (stain can mean dishonour or disgrace).
'l' inserted inside 'stain' is 'STALIN'.
Can you help me to learn more?
(Other definitions for stalin that I've seen before include "Soviet dictator, d. 1953" , "Mass-murderer" , "Dread dictator among Latins" , "Notorious dictator of Latins" , "Lenin's successor" .)