Fellow holding me back is evil genius (5)
I believe the answer is:
demon
'evil genius' is the definition.
(thesaurus)
'fellow holding me back' is the wordplay.
'fellow' becomes 'don' (both can mean an academic).
'holding' means one lot of letters goes inside another.
'back' says the letters should be written backwards.
'me' reversed gives 'em'.
'don' going around 'em' is 'DEMON'.
'is' is the link.
(Other definitions for demon that I've seen before include "Monster" , "beast" , "Devil - master performer" , "See 3" , "Fallen angel" .)