"The Simpsons" bus driver (4)
I believe the answer is:
otto
'the simpsons bus driver' is the definition.
(I've seen this in another clue)
This is all the clue.
(Other definitions for otto that I've seen before include "-- Klemperer, conductor" , "German man's name" , "Emperor's" , "Cooker" , "Rose produces this" .)