The 82-year-old said no-one could replace late actor John Thaw, who portrayed the Oxford detective between 1987 and 2000.
He said the UK’s love for the actor, who died in 2002 aged 60, meant his was the definitive screen take on the Morse novels.
He said: “Everybody is going to say nobody can do it half as well as dear old John could do it. This is what I did not want.”
Other high-profile fictional characters have been played by multiple actors, with James Bond being one example.
But Mr Dexter, who lives in Oxford, believes there was only one man for the job, and says he owns the intellectual rights to the character he created to prevent any other actor playing him.
He pointed to “ridiculous” casting of fictional detective Hercule Poirot before the “brilliant” David Suchet took the role as his own.
Mr Dexter said: “John said to me more than once ‘the best part he enjoyed playing on television was Inspector Morse’.”
He spoke ahead of an appearance at Oxford’s Pegasus Theatre’s Crime Night with series producer Chris Burt and Barrington Pheloung, the composer behind the music, to raise cash for youth projects.
The trio discussed their experiences working on the programmes.
Mr Burt said: “It is in his will – and his heart – that no-one can ever do Morse except for John Thaw.”
A younger Morse was played by Shaun Evans in this year’s pilot for Endeavour, backed by Mr Dexter, and more episodes are on the way.
There was also praise for the first Morse spin-off, Lewis, which began in 2006.
The comments came as filming finished two weeks ago for the seventh series.
Mr Dexter said of the crew: “What has surprised me and delighted me is the way people here develop a sort of camaraderie and friendship and love of this place Oxford.”
An ITV spokesman did not comment on Mr Dexter’s will but said: “We have absolutely no plans to remake Morse.”
Pegasus Theatre artistic director Euton Daley said of Thursday’s fundraising event: “It was a great evening for fans of crime fiction and TV and our thanks go to both of them.”
HOPES FOR MORE LEWIS
THE seventh series of Morse spin-off Lewis was widely expected to be the last.
But Morse series producer Chris Burt has revealed he had hopes for three, two-hour specials that could be broadcast in 2014.
Of the last day’s filming in Old Marston’s Victoria Arms, Mr Burt said: “It was all so full of warmth.”
The show stars Kevin Whately as Morse’s former sergeant Robbie Lewis, now a detective inspector, and Laurence Fox’s DS James Hathaway.
Viewing figures for the first three episodes of the most recent series attracted a total audience of 6.6m people, a share of 26 per cent of the viewing public.