The seat of that Bismarck fellow! (7)
I believe the answer is:
ottoman
'the seat' is the definition.
(ottoman is a kind of seat)
'that bismarck fellow' is the wordplay.
'that bismarck' becomes 'otto' (I am not sure about this - if you are sure you should give a lot more credence to this answer).
'fellow' becomes 'man' (I've seen this before).
'otto'+'man'='OTTOMAN'
'of' acts as a link.
Can you help me to learn more?
(Other definitions for ottoman that I've seen before include "Type of seat; Turkish" , "Low upholstered seat - relating to a Turkish dynasty" , "Am not to (anag)" , "Shared seat" , "showing Middle Eastern influence" .)