Superman creator's amazing zest in ideal position (9)
I believe the answer is:
nietzsche
'superman creator's' is the definition.
(I've seen this in another clue)
'amazing zest in ideal position' is the wordplay.
'amazing' indicates anagramming the letters.
'in' is an insertion indicator.
'ideal position' becomes 'niche' (I've seen this before).
'zest' with letters rearranged gives 'etzs'.
'etzs' inserted inside 'niche' is 'NIETZSCHE'.
(Other definitions for nietzsche that I've seen before include "German philosopher, d. 1900, noted for his concept of superman" , "German philosopher, wrote Beyond Good and Evil" , "German poet" , "19th century German philosopher who divided mankind into master class and herd" , "Friedrich -, nineteenth century German philosopher" .)