In a stern position, he presents a firm figure (3)
I believe the answer is:
cox
'in a stern position he' is the definition.
The answer is a person as well as being a singular noun. This is suggested by the definition.
'a firm figure' is the wordplay.
I cannot really see how this works, but
'firm' could be 'co' (a firm is a company) and 'co' is present in the answer.
A single letter 'x' remains which might be clued in a way I don't understand.
This explanation may well be incorrect...
'presents' acts as a link.
Can you help me to learn more?
(Other definitions for cox that I've seen before include "Helmsman" , "Boat's steerer" , "Steerer of oarsmen in rowing boat" , "Member of rowing crew" , "Passenger vehicle" .)