King of a wild horde (5)
I believe the answer is:
herod
'king' is the definition.
(I know that Herod is a king)
'wild horde' is the wordplay.
'wild' indicates an anagram.
'horde' anagrammed gives 'HEROD'.
'of a' is the link.
(Other definitions for herod that I've seen before include "King of Judea in the time of Jesus" , "NT king" , "Biblical king of Judea" , "King of Judaea, temple builder" , "Former king" .)