A life of someone by himself? (13)
I believe the answer is:
autobiography
'himself?' is the definition.
I can't tell whether this definition defines the answer.
'a life of someone by' is the wordplay.
'a life' becomes 'biography' ('biography' can be a synonym of 'life').
'of someone' becomes 'auto' (I am not sure about this - if you are sure you should believe this answer much more).
'by' is a charade indicator (letters next to each other).
'biography' after 'auto' is 'AUTOBIOGRAPHY'.
Can you help me to learn more?
(Other definitions for autobiography that I've seen before include "Memoirs" , "A person's account of their life" , "Story of one's life" , "Person's life story written by the subject" , "Personal account of one's life" .)