Gloria abused church boss (8)
I believe the answer is:
oligarch
'boss' is the definition.
(I know that oligarch is a type of ruler)
'gloria abused church' is the wordplay.
'abused' is an anagram indicator.
'church' becomes 'ch' (abbreviation on maps etc).
'gloria' anagrammed gives 'oligar'.
'oligar'+'ch'='OLIGARCH'
(Other definitions for oligarch that I've seen before include "powerful businessman" , "Mega-rich Russian with political influence" , "one of small group at top" , "Rich Russian with political influence" , "Powerful Russian?" .)