Warden puts on a stone; I don’t recognise him (8)
I believe the answer is:
stranger
'i don't recognise him' is the definition.
(a stranger is a person who isn't recognised)
'warden puts on a stone' is the wordplay.
'warden' becomes 'ranger' (I've seen this before).
'puts on' is a charade indicator (letters next to each other).
'a stone' becomes 'st'.
'ranger' put after 'st' is 'STRANGER'.
(Other definitions for stranger that I've seen before include "Outsider" , "visitor" , "someone making nuisance call?" , "More odd or wierd" , "'Weirder, odder (8)'" .)