Hard man becomes emperor (7)
I believe the answer is:
hadrian
'emperor' is the definition.
(Roman emperor)
'hard man' is the wordplay.
I cannot really see how this works, but
an anagram of 'hard' is 'hadr' which is within the answer.
'man' could be 'ian' (man's name) and 'ian' is located in the answer.
This accounts for all the letters.
This explanation may well be incorrect...
'becomes' acts as a link.
Can you help me to learn more?
(Other definitions for hadrian that I've seen before include "Roman emperor who visited Britain" , "Roman emperor and wallbuilder" , "Roman Emperor after Trajan" , "Roman emperor who built the British wall" , "Wall-building Roman emperor" .)