Roman emperor after Claudius (4)
I believe the answer is:
nero
'roman emperor after claudius' is the definition.
(I've seen this in another clue)
This is all the clue.
(Other definitions for nero that I've seen before include "Barbarous Roman emperor" , "Roman emperor infamous for his cruelty" , "Emperor said to have fiddled as Rome burned" , "Emperor said to have started the fire that destroyed Rome" , "Roman tyrant" .)