Rex Stout's stout sleuth Wolfe (4)
I believe the answer is:
nero
'rex stout's stout sleuth wolfe' is the definition.
(I've seen this in another clue)
This is the entire clue.
(Other definitions for nero that I've seen before include "Imperial Roman fiddler" , "Wicked fiddler" , "Emperor who played the fiddle" , "Roman emperor infamous for his cruelty" , "Roman emperor on the fiddle?" .)