Famous Red Square building’s fourth from the right (5)
I believe the answer is:
lenin
'famous red' is the definition.
'square building's fourth from the right' is the wordplay.
'square' becomes 'nine' (I've seen this before).
'building's fourth' becomes 'l' (I am not sure about this - if you are sure you should give a lot more credence to this answer).
'from the right' is a reversal indicator.
'nine'+'l'='ninel'
'ninel' reversed gives 'LENIN'.
(Other definitions for lenin that I've seen before include "Communist leader" , "Vladimir Ilyich Ulyanov, d. 1924" , "V. I. -, Soviet politician and revolutionary" , "First Soviet leader" , "Revolutionary man" .)