Among men, a rampaging Greek king (9)
I believe the answer is:
agamemnon
'greek king' is the definition.
(I've seen this before)
'among men a rampaging' is the wordplay.
'rampaging' indicates an anagram.
'among'+'men'+'a'='amongmena'
'amongmena' with letters rearranged gives 'AGAMEMNON'.
(Other definitions for agamemnon that I've seen before include "Gk. leader against Troy" , "Greek commander against Troy" , "Leader of Greeks in Trojan War" , "Greek hero, king of Mycenae" , "Greek leader in the Trojan War" .)