Service and sacrifice
In 2233, Lieutenant Kirk was serving as first officer aboard the USS Kelvin under Captain Richard Robau when it was diverted by Starfleet to investigate a mysterious singularity. The Romulan ship Narada, under the command of Captain Nero, emerged through the black hole from the year 2387 and began firing upon the Kelvin, severely damaging the ship.
When the Narada resumed firing, it became apparent that it never had any intention of negotiating a cease fire. Kirk followed the orders he was given and gave the order to abandon ship.
Among those being evacuated was Kirk's wife, Winona, who was aboard the ship and was going into labor with their son. She was to be evacuated and Kirk promised to join her shortly thereafter. Attempts to set the ship on autopilot failed, however, and Kirk was forced to remain on board to prevent the Narada from destroying the evacuation shuttles. He set the Kelvin on a collision course with the Narada.
In his last moments, Kirk was in contact with Winona as she gave birth to their son. They were trying to find a name for their child and Kirk suggested naming the baby after Winona's father, James. The last thing George Kirk heard before dying in the collision with the Narada were the cries of his newborn James T. Kirk. His sacrifice disabled the enemy ship and saved the lives of eight-hundred people.
Captain Christopher Pike wrote his dissertation on the Kelvin and George Kirk. Pike came to admire Kirk, describing him as a man who did not believe in "no-win scenarios" and as someone who had the instinct to leap without looking, a trait he felt Starfleet had lost by the 2250s.
Because Kirk died prematurely, James Tiberius Kirk never knew his father and thus never had an inspiration to join Starfleet. Instead, he spent his early years as a rebel and trouble-maker, until he was finally convinced by Pike to enlist in Starfleet and dared to do better than his father who had saved the lives of the crew of an entire ship; a dare Kirk would eventually satisfy by saving the entire Earth population and any other planetary population that otherwise might have been destroyed by Nero as the acting-captain of the USS Enterprise in 2258. (Star Trek)
George Kirk was played by Chris Hemsworth. Although Spock referred to George Kirk as being a lieutenant when he was killed, Kirk actually wore the rank braids of a lieutenant commander; Spock may have been abbreviating his rank in a non-traditional manner as lieutenant commanders are usually referred to as commanders. Deanna Troi and Shelby have also both been addressed as lieutenants (in "Encounter at Farpoint" and "The Best of Both Worlds, Part II", respectively) while clearly holding the rank of lieutenant commander.
He may have a brother, since James T. Kirk said he was staying at his uncle's farm in Star Trek Generations. It was never made clear which of his parents had a sibling though, or if he was just using the term for a long time family friend. In Star Trek, an uncle Frank was cut from the script and reworked into Winona's new husband heard in the film.
Intel's Star Trek tie-in website gave his serial number as SA-733-9624-AM.