When I mentioned the four Harry Mortons of the Burns and Allen TV show, it put me in mind of another TV character from the early days of TV who was recast three times so that four actors played the role in the space of only five years.
Martin Kane was TV's first private eye, and if I'm not mistaken, the first TV character to cross over into the four-color world of comic books. (Kane was a true multiversalist. He was also in the radio universe during the whole TV run, having debuted on radio only three weeks before his TV premiere.)
'Martin Kane, Private Eye' ran from September 1949 to June 1954, and was fully sponsored by the United States Tobacco Company. They made sure that most of the storyline took place at the local smoke shop so that its commercials could be integrated into the program. (I wrote about that aspect of the show once before.)
William Gargan was the first Martin Kane, playing the role for two years. This makes him the official version for Toobworld. He was followed by Lloyd Nolan, Lee Tracy, and finally Mark Stevens.
Like I said, Gargan was THE Martin Kane of Earth Prime-Time. But recastaways Nolan, Tracy, and Stevens were not quantum leapers, nor was Martin subjected to plastic surgery, "wish-craft", or impersonations by aliens or androids. And I don't think the "Arthur Dales" splainin from 'The X-Files' about siblings with the same name would be logical in this situation.
Instead, I'm calling on a simpler splainin for a far simpler time - Nolan, Tracy, and Stevens were the Martin Kanes from other Toobworlds.
Because he was the first replacement, Lloyd Nolan could be the Martin Kane from the Land of Remakes, for example.
As he once played the former President of the United States in the movie version of Gore Vidal's "The Best Man", I like the idea that Lee Tracy was the Martin Kane in the same TV dimension that housed 'The West Wing'. Perhaps he was also the Martin Kane from the dimensions for '24', 'Commander-In-Chief', 'Mr. President' & 'Hail To The Chief', and for the Movie Of The Week' TV dimension (which had a slew of alternate presidents.)
By the way, the picture above of Lee Tracy is probably from some other production, or just a generic publicity shot.....
And let me make this perfectly clear - I have nothing against Mark Stevens. I think he made a great private eye over in the Cineverse in a fun little noir called "The Dark Corner". But even the "Evil Mirror Universe" needs its own Martin Kane. (FYI: By the time Stevens took the role, the series underwent a name change to just 'Martin Kane, Detective'.)
So the detective show did a multidimensional tour of the TV Universe, starting out with Martin Kane on Earth Prime-Time and ending up in the evil dimension first introduced (or at least made popular) in 'Star Trek'.
Three years later, however, we revisited the private eye as played by William Gargan in 1957's 'The New Adventures Of Martin Kane'. So we were brought back full circle to the main Toobworld with this British production.