The mettle, we hear, of a man of iron? (5)
I believe the answer is:
metal
'iron?' is the definition.
(thesaurus)
'the mettle we hear of' is the wordplay.
'we hear of' indicates a 'sounds like' (homophone) clue.
'mettle' is a homophone of 'METAL'.
'a man of' acts as a link.
This may not be right. Some or all of it may belong to another bit of the clue.
Can you help me to learn more?
(Other definitions for metal that I've seen before include "Maybe lead" , "Iron, for instance" , "barium?" , "Gambling token" , "Copper, perhaps" .)