A sinister monk upsetting puritans (8)

I believe the answer is:

rasputin

I'm a little stuck... Click here to teach me more about this clue!

'a sinister monk' is the definition.
'rasputin' can be an answer for 'monk' (I've seen this before). I am unsure of the 'a sinister' bit.

'upsetting puritans' is the wordplay.
'upsetting' indicates an anagram.
'puritans' anagrammed gives 'RASPUTIN'.

Can you help me to learn more?

(Other definitions for rasputin that I've seen before include "Russian holy man who influenced a tsar" , "Puritans (anag) - Russian monk" , "Sinister adviser" , "Mystic who influenced the Romanovs" , "Notorious Russian monk at court of Tsar" .)

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