Unconventional nineties scientist (8)
I believe the answer is:
einstein
'scientist' is the definition.
(Einstein is an example)
'unconventional nineties' is the wordplay.
'unconventional' is an anagram indicator.
'nineties' anagrammed gives 'EINSTEIN'.
(Other definitions for einstein that I've seen before include "19 [BRAINY] fellow" , "Physicist who formulated theories of relativity" , "Brilliant physicist" , "Iconic theoretical physicist, d. 1955" , "Mastermind" .)