The cast and crew had gathered at the home of James Arness to watch the series premiere. They were not told in advance about the special introduction from John Wayne. Arness stated on the DVD commentary that he was very honored that his good friend, Wayne took the time to do this for him.
John Wayne appeared in the beginning to introduce the series. He was also originally offered the role of Matt Dillon but turned it down. And he recommended James Arness for the role.
A wanted poster on the wall in Matt Dillon's office reads: "William H. Bonney wanted for murder". William Bonney was also known as 'Billy the Kid', who was incidentally the one who committed the murder in the first radio episode. This poster puts the beginnings of Gunsmoke at 1881, or a little earlier. Bonney was killed in 1881. His real name was Henry McCarty and he took the name William H Bonney in 1877.
The title sequence (in the outside street, replaced by one with a painted backdrop in later seasons) shows Matt with his back to the camera vs. a black-hatted villain. Twelve seconds into the title sequence, the viewer can see Matt clearly draw before the villain. Later seasons' new sequence has the villain draw first.
Incidentally, Physicist Niels Bohr came up with a theory: the one who draws second moves faster because he reacts without thinking.
Psychologists at Birmingham University found Bohr was right, at least to a point. Volunteers averaged 10% faster when they drew second over first. Andrew Welchman's study found that while a gunslinger moved faster when they drew second, the difference was on average only 21 milliseconds - too slow to beat someone who had already pulled a gun. It appears to be accuracy, not who drew 1st that decides the victory.
According to James Arness on the DVD commentary, this was the first episode shown, but it was actually the second episode that they filmed.