Sinister controller (8)
I believe the answer is:
svengali
<span class="explanation-format__ClueExplanation">'<span class="explanation-format__original">sinister controller</span>' is the definition.<br/ ><span class="explanation-format__explanation">(I've seen this before)</span><br/ ><br/ >This is the entire clue.<br/ ></span>
(Other definitions for svengali that I've seen before include "Manipulative person" , "Person exerting sinister control over another" , "One exerting evil mental control over another" , "Trilby's mesmerist" , "Evil hypnotist in the George du Maurier novel, Trilby" .)