Extremely knavish, authoritarian old Turkic ruler (4)
I believe the answer is:
khan
'old turkic ruler' is the definition.
(historical title for a Turkish ruler)
'extremely knavish authoritarian' is the wordplay.
'extremely' says to hollow out the word (remove centre letters).
'authoritarian' becomes 'an' (I am not sure about this - if you are sure you should believe this answer much more).
'knavish' with its middle removed is 'kh'.
'kh'+'an'='KHAN'
(Other definitions for khan that I've seen before include "Imran --, cricketer" , "Title of respect in central Asia (for a descendant of Genghis?)" , "Title of rulers and officials in central Asia" , "Central Asian prince or chief" , "Central Asian ruler" .)