Choir gal could be one of few to exert control! (8)
I believe the answer is:
oligarch
'one of few to exert control' is the definition.
I can't tell whether this definition defines the answer.
'choir gal could be' is the wordplay.
'could be' is an anagram indicator.
'choir'+'gal'='choirgal'
'choirgal' is an anagram of 'OLIGARCH'.
Can you help me to learn more?
(Other definitions for oligarch that I've seen before include "Mega-rich Russian with political influence" , "member of small ruling class" , "Member of a small governing group" , "Member of ruling clique" , "Powerful Russian?" .)