King was a big deal to be sure, but if another mountie could make him cry "uncle" in terms of capturing the public's attention, it would be Sergeant William Preston of the Yukon. Arguably.
Originally titled "Challenge of the Yukon", Preston's adventures began as a radio show in early 1938 which lasted until 1955, at which point the television series began.
Despite having been on the air for over a decade, the show's name was only changed to Sergeant Preston of the Yukon in 1951 (which is also when the comic book began being published by Dell)...and therein lies the challenge I had with this character.
There's some question as to whether Preston really WAS the star of the show. It appears that the intent was for Preston's dog, Yukon King, to do the bulk of the work. Some of the comic book covers seem to support this...
...as does this page about the show.
Be that as it may, Preston (and his horse Rex completing the crime-fighting trifecta) was still a big deal. 29 issues of his comic book were published until its end, as well as the TV show's, in 1958. Along the way, Preston appeared in puzzles, a board game, and a number of giveaways as a result of a sponsorship agreement with Quaker Oats.
Entire episodes of the TV program are available on youtube, and can be purchased on DVD, but for kicks, here is the 1955 intro.