Origin of Commonwealth: memory expertly provided by this Commonwealth leader (8)
I believe the answer is:
cromwell
'this commonwealth leader' is the definition.
'Cromwell' can be an answer for 'leader' (Cromwell is an example). I'm not certain of the 'this commonwealth' bit.
'origin of commonwealth memory expertly' is the wordplay.
'origin of' suggests taking the first letters.
'memory' becomes 'rom' (ROM is an example).
'expertly' becomes 'well' (I can't explain this - if you can you should give a lot more credence to this answer).
The first letter of 'commonwealth' is 'c'.
'c'+'rom'+'well'='CROMWELL'
'provided by' acts as a link.
Can you help me to learn more?
(Other definitions for cromwell that I've seen before include "English general" , "Lord Protector (sixteen fifty three to sixteen fifty eight)" , "Thomas or Oliver?" , "Oliver, Puritan leader during 17th century English Civil War" , "Oliver --, Lord Protector" .)