Before "Gibbs" (Mark Harmon) became head of the "Major Case Response Team" at the "NCIS", he was a gunnery sergeant in the United States Marine Corps (USMC), a sniper, and an Iraq veteran. He experienced a real calamity very early in life.

His mother died when he was just 14 years old - at first, he thought she had died of cancer. Later, however, it turned out that she committed suicide so that her husband and son would not have to see her suffer any longer.

Mark Harmon as "Gibbs" in 'NCIS', 2003

NCIS: "Gibbs'" revenge and his journey

As it is often mentioned in NCIS, "Gibbs" lost his little daughter "Kelly" and his wife "Shannon". The two were killed in a car crash with a drug dealer.

Since then, it's been difficult for the agent to form new relationships and open up to people. Nevertheless, he was married three more times after that.

After the death of his wife and daughter, he took revenge on the killer and threw himself into his work. The agent assigned to his wife's case, "Michael Franks", who worked at the "NCIS", helped "Gibbs" get in.

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The bond between "Gibbs" and "Franks" grew stronger, and the agent saw him not only as his superior but also as a mentor and friend. However, "Gibbs" also had to say farewell to "Franks" eventually, as he was tragically shot and killed on the street.

NCIS: "Gibbs'" relationship with "Ziva David"

But "Gibbs" managed to develop strong relationships within his own team, namely with "Ziva David" and "Anthony 'Tony' DiNozzo". Especially in "Ziva", he always saw something like a daughter. When "Ziva" died, it broke his heart.

NCIS Season 17 Episode 10: "Gibbs" and "Ziva" have a heated exchange in a new teaser clip.

What he didn't know: "Ziva" faked her death. Meanwhile, she and "Gibbs" have managed to hunt down and kill "Ziva's" nemesis "Sahar", so that "Ziva" can now return to her family - to "Anthony DiNozzo" and their daughter "Tali".

NCIS: "Gibbs" and "Tony"

"DiNozzo" has always played a major role in "Gibbs'" life. At the beginning of their relationship, the two didn't even get along. "Gibbs even started to bully him.

But when Gibbs left the "NCIS" for some time and was drawn to Mexico, DiNozzo, of all people, became his successor. He took over command of the "NCIS Major Case Response Team".

But even this relationship was not meant to last: "Gibbs" had to say goodbye to Tony after a few years. After "Ziva" was declared dead, "Tony" moved to Paris with daughter "Tali" and left "Gibbs" at the "NCIS".

Mark Harmon and Michael Weatherly in NCIS.

"Leroy Jethro Gibbs" has been struggling with fear of commitment and separation anxiety for all of his life. But: When we look at "Gibbs'" tragic story so far, who can blame him?