John Thaw was aged 44 when he began playing Inspector Morse, but because of his prematurely white hair, many viewers thought he was about a decade older. Thaw was an alcoholic until 1994, and he often smoked up to three packs of cigarettes a day.
In Colin Dexter's original novels, Inspector Morse drove a Lancia. However, John Thaw, who had played Jack Regan on The Sweeney (1975), which featured a lot of Jaguars as villains' getaway cars, insisted that Inspector Morse would have driven an iconic British car, and never an Italian sports car. Dexter was so impressed with this reasoning that he asked his publishers to change "Lancia" to "Jaguar" in all subsequent reprints of his novels.
The main change between the original novels and the television series is that Inspector Morse's prurient and earthy interest in pornography and seedy striptease clubs is absent from the television version.
The opening notes of the theme music are based on the Morse code for the word "Morse", altered for musical purposes. The same notes are also included at the end and in places within the theme music. In the 1995 documentary "The Mystery of Morse: The Making of Morse", the composer stated that the theme sometimes spells the name of the murderer, a cryptic version of the name, or, as a red herring, an innocent character. However, there is nothing documented on the Internet for any specific name or episode. Morse code experts say that, aside from the code for "Morse", any other Morse code-like notes in the theme are complete gibberish, probably because the code was modified greatly for musical purposes.