Cruel king, but a hero to many (5)
I believe the answer is:
herod
'cruel king' is the definition.
(I've seen this before)
'a hero to many' is the wordplay.
'to many' becomes 'D' (Roman numeral for 500).
'hero'+'d'='HEROD'
'but' acts as a link.
(Other definitions for herod that I've seen before include "New Testament king" , "Infanticidal king" , "Ruler of Palestine when Jesus was born" , "King of Judea in the time of Jesus" , "Christ was born in the reign of . . . . . the Great (5)" .)