Bob Lilly is a great answer. It wasn’t him, but the guy was a champion athlete before he got into movies.
I’m running out of guesses, Burt Lancaster?
Scott
I really liked Burt Lancaster, but it wasn’t him.
With out googling it maybe Dale Robertson, he boxed?
Lee Marvin?
Scott
He wandered about under the stars a bit too much 
Clint Eastwood
No it wasn’t Clint Eastwood, Lee Marvin, or Dale Robertson.
What was the name of that guy who played Flash Gordon? Buster Crabbe?
Buster also played in a lot of cowboy movies. And he won a gold medal in swimming at the 1932 Olympics. He had a terrific physique.
I met Buster in 1974 at the Golden-Age Olympics in Sanford, Florida. Buster was a guest promoter and Arthur Jones got him to visit the Nautilus headquarters.
Buster Crabbe was the correct answer. Way to go Jeff.
My second favorite cowboy was Johnny Mack Brown. Anybody remember him?
Buster Crabbe played one tarzan movie also, I believe it was 1933
This thread gets me thinking that there were a good number of movie stars from back in the day that were impressively built and were good athletes. I think a lot of people were influenced by stars like that very much like Dr. Darden was, myself included. But I would differentiate them from those who were actual bodybuilders that had jumped into movies to capitalize on their physique, Arnold and Lou Ferrigno being prominent examples. Such people did not lift for their roles or to get into the business, but for the same reasons as most everyone, health and fitness.
Not sure if he ever did any Westerns, but William Smith was always someone that I thought was pretty impressive, and he maintained his strength and development for many years. Someone mentioned Charles Bronson, and he was another one that had good development for many years of his career, especially in the Great Escape.
This is in contrast to a lot of these modern actors, especially the ones in all these superhero movies, that do not train regularly or at all, but only train for the specific film/role, and then deflate back to normal afterwards. We see this quite a bit, and I would not be surprised if “enhancements” are utilized in a lot of cases.
I was mostly influenced as a child was by the greatest tarzan…johnny weismuller…
The Cowboys I was mostly influenced by was John Wayne, Glenn Ford, Clayton Moore and Lee Majors from the big valley…no fitness here, lol
Steve Reeves as Hercules was also a big influence
Bruce Lee was another huge influence
But the two that got me lifting was Lou Ferrigno on the Hulk and Arnold in Conan the Barbarian
As far as early TV Cowboys with imposing physiques go, Clint Walker stands out. But I was still pretty young when he had his greatest TV success. From my teenage years, Robert Conrad from the Wild Wild West was probably the most memorable. Not a particularly big guy, but he had that lean surfer look that seemed popular back then. Of course, there was Clint Eastwood. But you rarely saw him without a shirt. It wasn’t his physique that made him notable.
Not a cowboy but Sean Connery was a bodybuilder of some sort and I think he actually was in a physique contest or two ? My all time favorite cowboy though was Chuck Conners! Nobody in their right mind would mess with him. I still watch the Rifleman quite often! I had a Winchester made with the big loop like his that will fire rapidly like his did!!
Scott
I’ve got some old muscle magazines with Robert Conrad working out and doing his turned down wrist push-ups. I used to do those quite a bit at the time.
Scott
