Claudius I's successor (4)
I believe the answer is:
nero
'claudius i's successor' 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 "Emperor who played the fiddle" , "Roman emperor infamous for his cruelty" , "Imperial Roman fiddler" , "Roman 9" , "Barbarous Roman emperor" .)