This chap is a sombre sort (7)
I believe the answer is:
ambrose
'this chap' is the definition.
'a sombre sort' is the wordplay.
'sort' indicates anagramming the letters.
'sombre' with letters rearranged gives 'mbrose'.
'a'+'mbrose'='AMBROSE'
'is' acts as a link.
(Other definitions for ambrose that I've seen before include "Bishop of Milan once" , "Bishop-saint" , "saint, maybe" , "Church Father" , "-- Bierce, US author" .)