- "This guy is bad news. Terrorism, weapons, uranium, nukes. Someone's got to stop him."
- ―Jack McClane to his father, John.
John "Jack" McClane, Jr. is the youngest child of John McClane & Holly Gennero and brother of Lucy McClane. He is seen very briefly in Die Hard as a young boy and was only mentioned (sometimes only indirectly) in the series until the fourth sequel A Good Day to Die Hard, where he has now become an undercover CIA agent. He is the deuteragonist of the fifth film.
Jack has brown hair and grey eyes.
John "Jack" McClane, Jr. is the son of John McClane & Holly Gennero, born in 1984, he is the younger of two children, the other being his older sister, Lucy.
Jack appears briefly as a young child in one of the first films opening scenes. He and Lucy were playing in the kitchen when Lucy runs to get the phone because their mother calls. He would not be seen again after this (except in brief scenes featuring the family photo).
John, Jr. is mentioned by Thomas Gabriel who refers to him by his familiar name "Jack," noting that he goes by his mother's last name. Thus, in this film, he is actually John "Jack" Gennero.
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Jack McClane is the deuteragonist of the fifth installment. He is introduced as John's estranged son - at odds with, but cut from the same cloth as his father.
Jack was at a Moscow nightclub and killed a man named Anton, who was revealed to be an associate of corrupt high-ranking Russian official Viktor Chagarin. At the Russian prison, Jack makes a deal for a lighter sentence in exchange for his testimony on Komarov so he can get close to Komarov and save his life.
It is revealed that Jack is a CIA deep-cover agent on a three-year assignment in Russia to get evidence against Chagarin while getting government informant, Chagarin's ex-partner Yuri Komarov, to help to get evidence against Chagarin.
- In early drafts of the Live Free or Die Hard script, John, Jr. was originally named Jack and was set to be the hacker in that film who helped out McClane. This idea was later scrapped and instead, the character of Matt Farrell was written in.
- Jai Courtney was not the first pick for the role of Jack McClane in A Good Day to Die Hard. Other actors that were considered for the part included Aaron Paul, Ben Foster, Liam Hemsworth, James Badge Dale and Justin Timberlake.
- His name was revealed in the first film (21:23).