Mythical creature reportedly delivered gold to king (7)
I believe the answer is:
centaur
'mythical creature' is the definition.
(centaur is a kind of mythical creature)
'reportedly delivered gold to king' is the wordplay.
'reportedly' indicates a 'sounds like' (homophone) clue.
'delivered' becomes 'sent' (I've seen this in another clue).
'gold' becomes 'Au' (Au is the chemical symbol for gold).
'to king' becomes 'R' (abbreviation for rex, king in Latin).
'sent' is a homophone of 'cent'.
'cent'+'au'+'r'='CENTAUR'
(Other definitions for centaur that I've seen before include "Mythological man-horse" , "Mythical creature with horse's body and man's upper torso" , "Mythical semi-equine beast" , "Mythical hybrid" , "Mythical equine creature" .)