Jackson Gibbs is the father of Leroy Jethro Gibbs. After his son left to join the U.S.Marines, Jackson Gibbs continued to live in the town of Stillwater. He was widowed some years before the events in the sixth season episode "Heartland." possibly before Leroy met Shannon or shortly before Shannon and Kelly's Gibbs' funeral. During the episode "Frame Up", Gibbs mentions that his father painted pin-up girl Betty Grable on the nose of his P-51. From this, and Jackson's own remarks of "giving up the sky" in the episode "Heartland", it is possible that he had served in the US Army Air Corps during World War II and afterwards.
In Season 10, he was revealed to have an estranged friendship with Leroy Jethro Moore, who also acted as the partial namesake of his son.
Relationship with Leroy
Jackson Gibbs relationship with his son, Leroy Jethro has been strained for a long time. Jackson mentioned that he believed that it was Shannon who was responsible for sending him Christmas cards every year, after she and Jethro were married. The strain on their relationship between Jethro and Jackson was heightened by the fact that Jethro was upset and angry that Jackson brought a girlfriend to Shannon and Kelly's funeral. It was not until the conclusion of the sixth season episode "Heartland" that the two reconciled with each other.
A sign of the changing relationship between Jackson and Jethro occurred at the conclusion of the sixth season Christmas episode entitled 'Silent Night' when Jethro called Jackson to wish him a "Merry Christmas."
Jackson visited Gibbs for Christmas in the Season Seven Christmas episode Faith. When they got into a number of arguments, Gibbs asked Ducky to do some profiling, which turned out inconclusive. Jackson later admitted that he had been upset because his store had been robbed and he'd had to shoot the robber in self-defense.
In the season 7 finale, Paloma Reynosa who has a grudge against Gibbs for killing her father travels to Stillwater to kill Jackson. The episode ends in a cliffhanger with Paloma walking into Jackson's shop.
However, in the Season 8 debut episode, 'Spider and the Fly', it was shown that Gibbs had managed to warn Jackson of the Reynosa cartel's approach and as a result, Jackson was able to fight back against the cartel before escaping to Washington D.C., where he met up with Gibbs and Mike Franks.