Head of the top dog (8)
I believe the answer is:
director
I believe this clue is a double definition.
'head' is the first definition.
(director is a kind of head)
'the top dog' is the second definition.
(director is a kind of top dog)
'of' is the link.
(Other definitions for director that I've seen before include "Business manager or film maker" , "Managing board member" , "One who controls resources and expenditures" , "Senior person in a firm, executive or non-executive" , "Creditor made to create film or play" .)