Boundary rider in disguise remains unfamiliar (12)
I believe the answer is:
frontiersman
'boundary rider' is the definition.
The answer and definition can be both people as well as being singular nouns.
Perhaps there's a link between them I don't understand?
'disguise remains unfamiliar' is the wordplay.
'disguise' becomes 'front' (I can't justify this - if you can you should give a lot more credence to this answer).
'unfamiliar' indicates anagramming the letters.
'remains' with letters rearranged gives 'iersman'.
'front'+'iersman'='FRONTIERSMAN'
'in' acts as a link.
Can you help me to learn more?
(Other definitions for frontiersman that I've seen before include "Border dweller" , "pioneer" , "his position is borderline" .)