Revolutionary deserts his ship, ultimately presenting poser (5)
I believe the answer is:
pseud
'poser' is the definition.
(I've seen this before)
'revolutionary deserts his ship ultimately' is the wordplay.
'revolutionary' is a reversal indicator.
'deserts' becomes 'due' (I've seen this before).
'ultimately' indicates one should take the final letters.
The last letters of 'his ship' are 'sp'.
'due'+'sp'='duesp'
'duesp' back-to-front is 'PSEUD'.
'presenting' is the link.
(Other definitions for pseud that I've seen before include "Pretentious person (colloq.)" , "Poseur (colloq.)" , "Fraud -- dupes (anag)" , "Fake intellectual" , "Pretentious sort" .)