Ruler of star potential (4)
I believe the answer is:
tsar
'ruler' is the definition.
(I know that tsar is a type of crowned head)
'star potential' is the wordplay.
'potential' is an anagram indicator (another potential order of the letters).
'star' is an anagram of 'TSAR'.
'of' is the link.
(Other definitions for tsar that I've seen before include "Old leader" , "Person in charge" , "Tyrant" , "Russian ruler (S, not Z)" , "Alexander and Nicholas held this title in Russia" .)