Formal setting for a Trojan king (5)
I believe the answer is:
priam
'trojan king' is the definition.
(king of Troy in Greek mythology)
'formal setting for a' is the wordplay.
'formal' becomes 'prim' (I've seen this in other clues).
'setting for' indicates putting letters inside.
'prim' placed around 'a' is 'PRIAM'.
(Other definitions for priam that I've seen before include "Trojan king" , "Old king" , "Father of Paris in Troy" , "Old man of Paris" , "The last king of Troy, in Greek mythology" .)