Cares about having a ruler (6)
I believe the answer is:
caesar
'ruler' is the definition.
(Julius Caesar)
'cares about having a' is the wordplay.
'about' is an anagram indicator.
'having' is an insertion indicator.
'cares' anagrammed gives 'caesr'.
'caesr' going around 'a' is 'CAESAR'.
(Other definitions for caesar that I've seen before include "Roman ruler" , "Roman dictator" , "Old Roman leader" , "Julius, stabbed by Brutus" , "leader who acts like a dictator" .)