Countenance as hero? Not that man stopping below in extremis (4)
I believe the answer is:
brow
'countenance as hero? not that' is the definition.
'brow' can be an answer for 'countenance' (thesaurus). I am unsure of the remainder of the definition.
'man stopping below in extremis' is the wordplay.
'man' becomes 'ro' (I can't justify this - if you can you should give a lot more credence to this answer).
'stopping' indicates putting letters inside (inserted letters stop or plug a gap).
'in extremis' suggests removing the centre (the extremes of the word are used).
'below' with its middle removed is 'bw'.
'ro' placed inside 'bw' is 'BROW'.
Can you help me to learn more?
(Other definitions for brow that I've seen before include "Top of hill - part of face" , "Forehead or hill summit" , "intellectual level" , "Peak of a hill" , "Hill part -- head part" .)