First man, six-footer, resolute (7)
I believe the answer is:
adamant
'resolute' is the definition.
(both can mean determined)
'first man six-footer' is the wordplay.
'first' is a charade indicator (letters next to each other).
'man' becomes 'adam' (Adam is an example).
'six footer' becomes 'ant' (an ant has six feet).
'adam'+'ant' is 'ADAMANT'.
(Other definitions for adamant that I've seen before include "Unyielding, won't change mind" , "Unshakable (in an opinion)" , "Decided" , "unshakeable in purpose" , "Inflexible, obdurate" .)