Greek commander soon conceals ploy — the end of Priam (9)
I believe the answer is:
agamemnon
'greek commander' is the definition.
(mythical figure)
'soon conceals ploy the end of priam' is the wordplay.
'soon' becomes 'anon' (synonyms).
'conceals' indicates putting letters inside.
'ploy' becomes 'game' (both can mean a trick).
'the end of' says to take the final letters.
The final letter of 'priam' is 'm'.
'game'+'m'='gamem'
'anon' going around 'gamem' is 'AGAMEMNON'.
(Other definitions for agamemnon that I've seen before include "Greek commander against Troy" , "Legendary king" , "Fabled king soon" , "king of old" , "Leader of Greeks against Troy" .)