Buffett, per his nickname (6)
I believe the answer is:
oracle
'buffett per his nickname' is the definition.
(I've seen this in another clue)
This is the entire clue.
(Other definitions for oracle that I've seen before include "One successfully worked" , "ambiguous message" , "Medium for prophecy" , "O, clear off for the Greek wise man" , "Augur - prediction" .)