The first American, not quite so unappreciated (9)
I believe the answer is:
thankless
'quite so unappreciated' is the definition.
'thankless' can be an answer for 'unappreciated' (synonyms). I'm not sure about the 'quite so' bit.
'the first american not' is the wordplay.
'the first american' becomes 'thank' (I am not sure about this - if you are sure you should believe this answer much more).
'not' becomes 'less' (I've seen this in other clues).
'thank'+'less'='THANKLESS'
Can you help me to learn more?
(Other definitions for thankless that I've seen before include "Receiving no appreciation" , "Unappreciated" , "Showing no gratitude" .)