He is at the back of the room (5)
I believe the answer is:
denis
'he' is the definition.
(I've seen this before)
'is at the back of the room' is the wordplay.
'at the back of' is a charade indicator (letters next to each other).
'the room' becomes 'den' (den is a kind of room).
'is' after 'den' is 'DENIS'.
(Other definitions for denis that I've seen before include "Patron saint of France" , "St -, first Paris bishop" , "- Healey, former Chancellor of the Exchequer" .)