Clue: Past peak, supporting amateur actor, bitter leading man (5,4)
Answer: ALPHA MALE
Explanation: Definition: leading man
 [ ALP(a peak/a high mountain) **placed above**(Past …, in a down clue) + HAM(an amateur, and hence bad, actor) **placed above**(supporting …, in a down clue) ] ALE(a bitter beer).
My best shot at explaining "past" and "supporting".
Defn: …/the dominant male in a particular group.