Great politician spoken of as an important person (6)
I believe the answer is:
bigwig
'important person' is the definition.
(bigwig is a kind of important person)
'great politician' is the wordplay.
'great' becomes 'big' ('big' can be a synonym of 'great').
'politician' becomes 'wig' (I can't justify this - if you can you should give a lot more credence to this answer).
'big'+'wig'='BIGWIG'
'spoken of as an' acts as a link.
I am not very happy about this link. Some or all of it may be part of another bit of the clue.
Can you help me to learn more?
(Other definitions for bigwig that I've seen before include "Person of some importance" , "Important person with large toupee" , "important figure" , "Luminary" , "Important person (slang)" .)