Overall chief (7)
I believe the answer is:
supremo
<span class="explanation-format__ClueExplanation">'<span class="explanation-format__original">overall chief</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 supremo that I've seen before include "big Daddy" , "Champion" , "Top dog" , "Leader with unlimited powers" , "Overall chief" .)