Nice one! Actor Martin ultimately perfect for Shaggy (7)
I believe the answer is:
unkempt
'shaggy' is the definition.
(thesaurus)
'nice one actor martin ultimately perfect' is the wordplay.
'nice one' becomes 'un' ('one' in French, eg in Nice).
'actor martin' becomes 'kemp' (I am not sure about this - if you are sure you should give a lot more credence to this answer).
'ultimately' says to take the final letters.
The last letter of 'perfect' is 't'.
'un'+'kemp'+'t'='UNKEMPT'
'for' acts as a link.
Can you help me to learn more?
(Other definitions for unkempt that I've seen before include "shabby" , "Slovenly" , "Rough and ragged" , "Not properly cared for" , "Tangled and untidy, as hair may be" .)