Man of iron, maybe, though at heart a bighead (5)
I believe the answer is:
robin
'man' is the definition.
'iron maybe though at heart a bighead' is the wordplay.
I cannot really understand how this works, but
'maybe' could be 'i' (I've seen this in other clues) and 'i' is found in the answer.
'bighead' could be 'b' (head letter of 'big') and 'b' is present in the answer.
'at' could be 'on' (location) and 'on' is present in the remaining letters.
A single letter 'r' remains which might be clued in a way I don't see.
This explanation may well be incorrect...
'of' is the link.
Can you help me to learn more?
(Other definitions for robin that I've seen before include "Bird - boy's name" , "So-called outlaw" , "Christmas songbird" , "Day was one" , "Batman's helper" .)