In the third season of Star Trek, "Spectre of the Gun" stands out because it sent the Enterprise crew into the Wild West, where they discover it's the exact date of the history-making gunfight at the O.K. Corral.

Immediately in the episode, the Enterprise crew gets mistaken for the Clanton gang, the opposing group famously involved in this fight, pitted against Doc Holliday as well as the famous lawmen Virgil Earp and his brothers Wyatt and Morgan.

For this episode, Chief Medical Officer Dr. McCoy falls into the shoes of Tom McLaury, a Clanton outlaw who history knows definitely died at the O.K. Corral shoot-out, and this is the fate that the Enterprise crew must try to avoid if they wish to save their own necks on Star Trek.

What you may not realize is that the actor who plays Dr. McCoy, DeForest Kelley, had been to the O.K. Corral before, not once, but twice.

Kelley first visited the O.K. Corral playing one of the Clantons in a 1955 episode of the TV series You Are There, but he more famously played one of the Earp brothers in the sensational 1957 Western blockbuster Gunfight at the O.K. Corral.

In 1957, a Los Angeles Times critic praised this movie as being on par with some of the genre's best like Shane and High Noon, writing, "The more discriminating moviegoer as well as the avowed Western fan will have little hesitancy in putting his OK on Gunfight at the O.K. Corral."

Kelley featured in this movie alongside a star-studded cast that saw Kirk Douglas as Doc Holliday, Burt Lancaster as Wyatt Earp, and playing the Cowboys, as the Enterprise crew did, was the "largest assortment of certified badmen yet rounded up for a single Western," including Lee Van Cleef and Dennis Hopper.

This memorable Western was nominated for two Oscars, and for Kelley, it was a major turning point in his acting career, which up to that point had been such a failure that he was considering quitting acting altogether.

By 1960, Kelley's career had turned around, though, and he was no longer seen as someone who only played heavies in Westerns, but now viewed as an actor with range.

Finally, he was considered someone to watch at 40 years old. Before that he was only known for having clean fingernails.

"While you may not recognize the name," a critic in The Oakland Tribune wrote, "Kelley's face is familiar on TV. He invariably plays the role of a sleek, cunning hoodlum who always stands outside the door, paring his fingernails, with an evil eye on the hero. Because of this Kelley is known as having the cleanest fingernails in Hollywood."

Gunfight at the O.K. Corral helped Kelley break out of what The Kansas City Star reported in 2005 he considered his only way forward as an actor until then: "His fate was the bad hombre, and his genre was the Western."

Of course, a lot of that break-out from Westerns had to do with meeting Leonard Nimoy and Gene Roddenberry on the sets of Westerns, so that when Roddenberry was ready to create Star Trek, he had both actors already in mind.

Originally, he wanted Kelley for Spock.

Kelley saw his future more in Bones, though, and in "Spectre of the Gun," fans can consider the episode a tribute to how the O.K. Corral enabled Kelley's rise to stardom.