Previous emperor taxed leader who was not obliged to pay (6)
I believe the answer is:
exempt
'not obliged to pay' is the definition.
(I've seen this in another clue)
'previous emperor taxed leader who' is the wordplay.
I cannot quite understand how this works, but
'previous' could be 'ex' (prefix meaning former or onetime) and 'ex' is present in the answer.
'leader' could be 'e' (I've seen this in other clues) and 'e' is found in the answer.
This may be the basis of the clue (or it may be nonsense).
'was' is the link.
Can you help me to learn more?
(Other definitions for exempt that I've seen before include "Absolve, excuse" , "Freed from obligation, tax etc" , "Not subject to, taxation say" , "Free (from taxes, etc)" , "Free (from, eg, taxes)" .)