George Samuel "Sam" Kirk was a male Human scientist in the 23rd century. He was married to Aurelan and they had three sons, including Peter. He was the brother of famed Starfleet Captain James T. Kirk, who was the only one who called him "Sam".
In 2265, George saw James off when the captain began a five-year mission of exploration in command of the USS Enterprise. Also saying farewell were Aurelan and their three sons. On this occasion, Sam mentioned that he wished to be transferred to the Earth Colony II research station. (TOS: "What Are Little Girls Made Of?")
Sam was a research biologist living with his family on Deneva the following year, when vessels from Ingraham B arrived carrying flying parasites. Many of the colonists, including Sam, were attacked and infiltrated by the parasites. Resisting the parasites' control was excruciatingly painful, but in early 2267, eight months after the Ingraham B vessels arrived, Aurelan managed to break the long communication blackout and get a brief distress call out to the Enterprise. By the time the ship arrived, Sam was dead; his wife died soon after. Their son, Peter, lived and was ultimately freed of the parasites. (TOS: "Operation -- Annihilate!")
The corpse of George Samuel Kirk was portrayed by William Shatner with a mustache and a different hairstyle. This was the only time that Shatner portrayed a character other than James T. Kirk (or Kirk's body being invaded or mimicked by another being).
George Samuel Kirk was to appear in 2009's Star Trek (referred to in the film's script as "George Kirk, Jr." ), where he would have been played by Spencer Daniels. Scenes featuring Daniels as Sam Kirk were filmed, but the character was entirely cut from the final release. The one remaining scene of Daniels playing Sam Kirk, in which Jim Kirk called out to him as he was driving past him in their uncle's (in the final cut, their step-father's) Corvette, was altered to change the name of Daniels' character to "Johnny", apparently a friend of Jim's.
George Samuel Kirk's deleted scene from 2009's Star Trek was available on Star Trek the two-disc DVD release for the film, Star Trek the three-disc Blu-ray release as well as the Blu-ray set Star Trek: The Compendium. In the scene, George ran away from home and his brother to escape the cruelty of their uncle Frank, finding it impossible to "be a Kirk" in Frank's household. He was also angered that Frank had claimed their late father's Corvette as his own. After George left, Jim found the keys to the Corvette and drove off in the car. As originally conceived, Jim drove by and called out to a shocked George, who had been trying to hitchhike.
George Samuel Kirk appeared in the last chapter of Star Trek: Enterprise novel Last Full Measure, set in 2238, in which an elderly Trip's first visit to the Starfleet War Memorial coincided with that of young Sam and Jimmy Kirk, rendering the quiet reflection he had hoped for an impossibility. The scene established George's birthdate August 12, which was also when Federation Day was celebrated. However, according to "Echoes of Yesterday" in TOS Special 3, George's birthdate was September 7, 2229, and his death took place on April 13, 2267. ("Operation – Annihilate!" originally aired on April 13, 1967)
A slightly altered version of George's deleted scene from 2009's Star Trek was found in the film's novelization. Among the scene's changes made for the book was George's revelation that Frank (who in a merger of the script and film characters the boys' stepfather, not uncle) wanted Jim to wash the Corvette, which had belonged to their late father, because he intended to sell it behind their mother's back - it was after hearing this that the decision to steal the car was made.
The alternate reality George appeared in IDW Publishing's Star Trek: Ongoing comic series, exploring events of the original series in the alternate reality, which clarified that the boys lived with their uncle until George ran away to live with his grandfather. This later led to a rift between the brothers, James feeling that George had abandoned their mother.
During their investigation of the neural parasites, Kirk and the crew discovered George living underground with his family to escape the influence of the parasites after their attack on the colony, with the Enterprise subsequently devising a means to banish the parasites and cure George's family, which here consisted only of his wife Aurelan and one son, Peter (β). At the story's conclusion, George and his family return to the colony, with George complimenting his brother's success, a degree of reconciliation having been reached between the two of them.
His mirror universe counterpart (β) was mentioned as being a Terran Empire scientist in the short story "The Greater Good" contained in the anthology Shards and Shadows. In 2263, he was awarded the Zee-Magnees Prize for his work in precision frontal lobotomy. As he had no interest in a military career and his brother James T. Kirk had no interest in science unless he could manipulate it to make his life easier, neither brother had to worry about the other getting in the way of his career and having to be eliminated.