Star Trek: Strange New Worlds Season 3 is set around 2260, meaning Kirk and Spock are not yet the best of friends, or the greatest duo in history. Surprisingly, though Kirk is not without a best friend, at this point. Star Trek: The Original Series was responsible for the greatest duo in history, but before there was Kirk and Spock, there was Kirk and Lt. Gary Mitchell.
Lt. Gary Mitchell was Captain Kirk's best friend and appeared on-screen for one single episode, Episode 3 of the first season of Star Trek: The Original Series, which is set in 2265. Mitchell was a lieutenant commander on the USS Enterprise, and he was serving under Captain Kirk.
Here's everything about Captain Kirk and Lieutenant Gary Mitchell's friendship that will be explored in Star Trek: Strange New Worlds.
Captain Kirk's best friend before Spock in Star Trek: Strange New Worlds Season 3

Star Trek: Strange New Worlds can explore Kirk and Mitchell's friendship in Season 3 as it is based around the same time, before we're taken through the start of the friendship for the iconic duo (Kirk and Spock). Kirk and Mitchell met in the Starfleet Academy Days in the early 2250s, and the two developed a great friendship. Mitchell, a student in Kirk's class, had heard about Kirk's above-par expectations before he ever attended his class.
Mitchell described Kirk as a "stack of books with legs" when fondly looking back at their Starfleet days, and even talks about a blonde girl whom he introduced Kirk to to get him distracted and make his classes easier to get through.
These fond memories prove that these two had a great friendship, which might be explored in Star Trek: Strange New Worlds. Especially considering that Mitchell was a part of Kirk's crew because Kirk had personally requested him. Both Kirk and Mitchell have saved each other's lives on numerous occasions while they're on missions together. Once, Mitchell almost died saving Kirk's life after he took a poisonous dart that was intended for Kirk.
On their final mission, Kirk led the Enterprise to the place where SS Valiant, a vessel that had disappeared 200 years ago, was last seen. In exploring that location, the Enterprise crossed the galactic barrier. In doing so, Mitchell's ESP was supercharged by the energy field, making him a danger to the entire crew, including Kirk. Mitchell had to be killed by Kirk so that humanity could be safe. Star Trek: Strange New Worlds has the opportunity to fill in the blanks in Kirk and Mitchell's friendship as well as their shared tragic history.

There is no update at the moment on whether Star Trek: Strange New Worlds is going to be bringing in an updated version of Mitchell in or not, but an exploration of this deep friendship would be great. This would also give them a chance to deeply explore the emotions behind Kirk being forced to kill one of his best friends. It would also lead to Kirk and Spock's friendship, which Ethan Peck, in conversation with Screen Rant, described as:
"platonic love at first sight"
It will be exciting to witness Spock and Kirk's friendship grow as they were introduced in Season 2 of Star Trek: Strange New Worlds.
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