Good character to ruin, one in the grip of the devil (9)
I believe the answer is:
samaritan
'good character' is the definition.
The answer and definition can be both people as well as being singular nouns.
Perhaps they are linked in a way I don't understand?
'ruin one in the grip of the devil' is the wordplay.
'ruin' becomes 'mar' (I've seen this before).
'one' becomes 'I' (Roman numeral).
'in the grip of' is an insertion indicator.
'the devil' becomes 'satan' (synonyms).
'mar'+'i'='mari'
'mari' put inside 'satan' is 'SAMARITAN'.
'to' is the link.
Can you help me to learn more?
(Other definitions for samaritan that I've seen before include "One offering help to the suicidal" , "Charitable person" , "Helpful chap" , "Counsellor" , "Good person who helps another in distress" .)