Ward Bond (Major Seth Adams) and Robert Horton (Flint McCullough) did not get along on the set. According to Horton, Bond spread rumors about his sexuality. The two men settled their differences two days before Bond died.
Although it was not publicly disclosed at the time, Ward Bond was already in terrible health when the series began. He was ill with high blood pressure, and had been ordered to reduce his workload. However, he continued to drink heavily while working on the series.
Gene Roddenberry described his original concept of Jornada nas Estrelas (1966) as "Wagon Train to the Stars." Gene L. Coon (the writer/producer who invented the Klingons and developed many other elements of the Star Trek universe) wrote 23 episodes of Wagon Train.
Onscreen Ward Bon and Robert Horton had an almost father-son relationship, though they did not always appear together; episodes tended to feature one or the other in alternate weeks. But off-screen they often clashed. After one particularly fierce argument, the two men vowed not to appear together on camera again. (They did weeks later, however, when the script called for it.)
This show was preceded by the film Caravana de Bravos (1950) in which Ward Bond played the head of a group of families traveling by wagon train. He did not play the same character but it served as the inspiration for the series.