James T. Kirk/Relationships/Family/Sam Kirk

George Samuel Kirk (called "Sam" only by his brother) was also, for a time, a Starfleet officer. ()
Their relationship did experience signs of strain at times; Sam expressed feelings of jealousy towards James' quick rise. In 2259, James had become the first officer on the Farragut, the youngest in Starfleet history, a record previously held by their father. Sam felt James' ambition and brash attitude reflected badly on him. ()
Sam later described Una Chin-Riley to James as "the first officer that James thought he should be like." Someone who kept a necessary distance from her crew because she knows she has to make hard decisions. ()
Sam, along with his wife Aurelan and three sons, joined his younger brother for a farewell visit before the Enterprise departed for her five-year mission. It was the last time Jim saw Sam alive. () Sam ended up on Deneva, with his wife and son Peter by 2267. James was too late to save his brother and sister-in-law from the neural parasites that had invaded Deneva that year, and killed the couple, but Peter survived the attack. ()
According to an alternate timeline version of Sam Kirk, he described Jim as a "huge pain in the ass but he's a fine a captain as Starfleet has." ()