Mark, the Spanish officer (7)
I believe the answer is:
colonel
'officer' is the definition.
(colonel is a kind of officer)
'mark the spanish' is the wordplay.
'mark' becomes 'colon' (colon is a kind of mark**).
'the spanish' becomes 'el'.
'colon'+'el'='COLONEL'
(Other definitions for colonel that I've seen before include "soldier" , "'No cello for this officer, strangely (7)'" , "Bogey perhaps" , "Comissioned military officer" , "Commander" .)