Cecil answered this question back in 1976 as follows:
A Straight Dope Classic from Cecil’s Storehouse of Human Knowledge
What was the name of Dudley Do-Right’s horse?
April 30, 1976
Dear Cecil:
One evening during an orgy of hard-core trivia, we were suddenly and frustratingly stumped by a truly baffling item. Even the most devoted trivia freaks among our friends drew blanks when we presented them with this one. If you can answer it for us, Cecil, we’ll finally be able to sleep nights. What they hell was the name of Dudley Do-right’s horse?
— The Smithies, Chicago
Dear folks:
Dudley’s horse was named Horse. That’s it — Horse. Bet you could kick yourself, huh? Now you can go back to worrying about the important things in life, like the Middle East situation, world hunger, and where Bullwinkle went to college. Answer on request.
I am here to say that his answer is not correct. However; the only evidence I have is that of an eye-witness. I saw the original episode that gave the name of Dudley’s horse and it was a very specific and blatant event in the episode.
The reason being is that his horse had a fairly sophisticated name. Much contrary to the other names in the series; like Snidely Whiplash, and Nell Fenwick.
The episode announcing the horse’s name only aired once that I know of, either in 1964 or 1965. The only reason I remember it (after years of grappling for the memory) is that the name was the same as another TV person associated with another popular TV show at the time.
The Horse’s name is Maurice. I remembered it because it is the same name as Samantha’s father in the original TV Series: Bewitched, that was on during the same period, and I made that connection at the time.
The reason there is so much controversy about this is that I am not the only one who saw that episode, and because of the interest, (and increased demand) the producers and writers of the Dudley cartoon wouldn’t say one way or the other.
The trivia question first surfaced (or the first time I heard it) back in 1975. Again, without verifiable evidence, I know this doesn’t count for much, but its all I have.
The answer “Horse” came from this lack of verifiable evidence. Not because its what Dudley called him. He referred to him as “my horse”, and Nell and her father, (even Snidely) referred to him as “Dudley’s Horse”, or “your horse” when speaking to Dudley.
So for those who want it, there it is. 45 years later.