There was nothing fancy about the opening credits of Gunsmoke when the Western first rode onto TV screens on September 10, 1955. However, audiences loved the striking 15-second sequence of U.S. Marshal Matt Dillon thundering across rugged terrain atop his powerful horse. That horse, a beautiful buckskin Thoroughbred named Buck, quickly became as much a part of the show’s identity as James Arness himself.

For two decades and 635 episodes, Arness was most often partnered with Buck, a horse chosen for practicality. “Buck was chosen not because of his intellect or his fidelity, but because he is very large and only a very large horse will fit me,” Arness once joked, according to INSP. “You’ll never catch Buck doing calculus on Gunsmoke. Confidentially, Old Buck is kind of stupid. Can’t even count to four.”