Philosopher is to alter in translation (9)
I believe the answer is:
aristotle
'philosopher' is the definition.
(Aristotle is an example)
'is to alter in translation' is the wordplay.
'in translation' indicates anagramming the letters (I've seen this in other clues).
'is'+'to'+'alter'='istoalter'
'istoalter' with letters rearranged gives 'ARISTOTLE'.
(Other definitions for aristotle that I've seen before include "Thinking Greek" , "Greek philosopher, pupil of Plato, tutor of Alexander the Great" , "Totaliser (anag) - ancient Greek" , "noted thinker" , "Greek philosopher (Poetics, Politics)" .)