Unconventional nineties genius (8)
I believe the answer is:
'genius' is the definition.
(I've seen this before)
'unconventional nineties' is the wordplay.
'unconventional' indicates an anagram.
'nineties' anagrammed gives 'EINSTEIN'.
(Other definitions for einstein that I've seen before include "Nobel prize-winner" , "Disney's 14 [GREAT DANE]" , "Father of Relativity" , "renowned scientist" , "Scientific genius" .)