Star Trek: The Original Series’ Captain James T. Kirk (William Shatner) is one of the most iconic characters in all of Star Trek, represented by plenty of great episodes. TOS' initial rejected pilot episode, "The Cage," did not feature Kirk, but instead Jeffrey Hunter's version of Captain Christopher Pike and a largely unrecognizable ing cast, other than an unusually emotional Spock (Leonard Nimoy). The show's tone and cast were overhauled for the show's second pilot episode, "Where No Man Has Gone Before," with Kirk's charm and dynamism immediately on display.

Captain Kirk has proven to be one of the most enduring characters in all of Star Trek. Not only were his adventures chronicled in Star Trek: The Original Series, but also in the film franchise that followed, as well as in the rebooted Kelvin timeline films, where he was played by Chris Pine. But the heart and soul of James T. Kirk was born on TOS, and he features prominently in some of the most celebrated science fiction stories of all time.

8 "The Enemy Within"

On a routine mission, the USS Enterprise's transporter malfunctions, splitting Captain Kirk into good and evil versions. This is the first episode of the series where Shatner's performance goes over the top in a way the actor is often mocked for. But it works here, as he fully embraces the chaos and insanity of the darker Kirk, a mesmerizing performance that set the tone for the emotional beats Kirk's capable of hitting. "The Enemy Within" also introduces the classic trope of the transporter accident, which would go on to become a plot point in many series, including Star Trek: The Next Generation's "Realm Of Fear" and Star Trek: Voyager's "Tuvix."

7 "Mirror, Mirror"

Another episode where Shatner plays two versions of Kirk, "Mirror, Mirror" introduces the concept of the Mirror Universe, an alternate reality where the Federation is replaced by the brutal Terran Empire, with Kirk as one of its despotic leaders. Kirk is forced to assume the role of the Mirror Universe Kirk when a transporter malfunction sends him and a handful of his crew to the dark reality. Shatner's versatility is on full display as he gets to play a tense game of cat and mouse as the real Kirk in the Mirror Universe, while he gets to mug it up as the evil doppelganger trapped in the main timeline.

6 "The Trouble With Tribbles"

One of the lightest episodes of Star Trek: The Original Series, "The Trouble With Tribbles" sees the USS Enterprise overrun with the titular furry creatures while also dealing with a nefarious Klingon plot. Loose and casual throughout the episode, Kirk is never more appealing than he is here, a good-natured man just trying to get a chicken sandwich without a living fur ball in it. The scene where hundreds of Tribbles tumble down onto Kirk from a cargo hold is one of the more iconic images of the entire series. "The Trouble With Tribbles" is proof that Kirk can be perfectly charming and engaging even when the stakes aren't sky-high.

5 "Errand Of Mercy"

"Errand Of Mercy" sees the debut of the infamous villains the Klingons, with whom the Federation finds itself on the brink of war with. Kirk is ordered to protect the peaceful planet of Organia from being used as a Klingon base of operations. To Kirk's surprise, the simple Organians are unconcerned with the Klingon occupation of their planet. Kirk's resentment for the Organians almost seems to outweigh his hatred of the Klingons, until it's revealed the Organians are an impossibly advanced race of beings who abhor violence. The Organians prevent the Federation and Klingons from going to war, much to Kirk's bemusement.

4 "Where No Man Has Gone Before"

After the show's original pilot, "The Cage," was rejected by network NBC for being "too cerebral," things got a lot more fun and exciting with the show's second pilot, "Where No Man Has Gone Before." The newly added Kirk is immediately fun to watch and easy to root for. His rapport with Spock in the episode's opening scene solidifies a relationship that would last for decades. Kirk's climactic battle with his possessed friend Gary Mitchell (Gary Lockwood) would cement Kirk's reputation as a man of action, just as willing to use his fists as his mind. "Where No Man Has Gone Before" is a pitch perfect introduction to Kirk.

3 "Arena"

"Arena" is often ridiculed for a couple of aspects that have aged poorly, but it's a harrowing episode. After a Federation outpost is destroyed, Kirk is forced into one-on-one battle with a vicious Gorn Captain responsible for the massacre by the advanced race known as the Metrons. The fight is incredibly slow and drawn out, the choreography leaves much to be desired, and the Gorn costume is frankly ridiculous. And yet it's an engrossing hour of television, as Kirk uses all of his wits and strength to outsmart the lumbering monster intent on killing him. Kirk grants the defeated Gorn mercy, ending the conflict and surprising the Metrons.

2 "The City On The Edge Of Forever"

After a crazed Dr. Leonard "Bones" McCoy (DeForest Kelley) travels back in time via the Guardian Of Forever, Kirk and Spock are forced to follow him to repair some cataclysmic damage he does to the timeline. Kirk and Spock find themselves in depression-era America where they meet Edith Keeler (Joan Collins), who ran a soup kitchen and had unusual insight into humanity's potential. Kirk eventually falls in love with Edith, who Spock deduces must die to restore the timeline. Kirk watches in horror as Edith dies in a traffic incident, powerless to save the woman he loves. The timeline is restored, but it's an empty victory for Kirk.

1 "Balance Of Terror"

Arguably the single best episode of Star Trek: The Original Series, "Balance Of Terror" sees Kirk face off with the mysterious Romulans, with the two sides on the brink of war. Kirk's quiet confidence is palpable as he masterfully outmaneuvers his Romulan counterpart (Mark Lenard) while calming a nasty bit of bigotry on the USS Enterprise when it's revealed Vulcans and Romulans are biologically identical. It's one of Shatner's more understated performances, but it's infused with so much tension and intrigue that it stands head and shoulders above the rest. "Balance Of Terror" is Captain James T. Kirk at his finest.