Among men, a rampaging Greek king (9)
I believe the answer is:
agamemnon
Here is my best explanation:
'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'.
This clue was last seen in The Telegraph