He played Superman, note, whom film was all about (5)
I believe the answer is:
reeve
'he played superman' is the definition.
(I've seen this in another clue)
'note whom film was all about' is the wordplay.
I cannot quite understand how this works, but
'note' could be 're' (as in do-re-mi) and 're' is located in the answer.
The remaining letters 'eve' is a valid word which might be clued in a way I don't understand.
This may be the basis of the clue (or it may be nonsense).
Can you help me to learn more?
(Other definitions for reeve that I've seen before include "Bailiff, steward" , "Pass the end of a rope through the bailiff" , "Anglo-Saxon magistrate - female bird - pass (a rope) through a hole" , "Someone with a tale" , "Medieval official - pass rope through an eye" .)