NCIS, a CBS crime procedural that premiered in 2003, has been a smash success in both crime procedurals and entertainment in general since its debut. 

Characters, however, leave after such a long run. The departed NCIS cast has offered a number of explanations for their characters' exits or deaths from the program --from plotlines running their course to cast member clashes that unfortunately sour ties.The backstory is as intriguing as the cases that Special Agent Leroy Jethro Gibbs and his team of NCIS experts have solved.

With that in mind, here's everything we know about the main cast members who have departed NCIS, as well as the reasons for their departure.

Why did Cote de Pablo Leave NCIS? 

Following the departure of Special Agent Todd, the writers agreed that the show needed another female character, and Cote de Pablo was the solution.

The former Mossad agent first joined the team in the third season and has since been a crowd favorite. From her absolute badassery and outstanding talents to her ability to stay calm under pressure, she's the kind of solid, autonomous female protagonist we've all wished for.

Despite this, she left the show after nine seasons, making her the first of the main characters to depart from NCIS. 

The actress said she quit for personal reasons at the time, but it was later revealed that she didn't like the direction the writers were taking her character in. 

De pablo admitted in a 2016 interview that her character's growth, or lack thereof, didn't strike the right note with her. They were going to take her back to Israel and make her an unfortunate wretched lady, she told Cinema Blend.

"I said well what do I leave all the women who have watched and followed the show? I didn't think it was fair," she said. 

Ziva is killed off at the conclusion of season 10, leaving Anthony DiNozzo as the single parent of a girl he had no idea existed.

Despite her departure from the programme, de Pablo was open to reprising the role if it was performed in a professional manner. "Until anyone would really write something amazing about her," the actress admitted, she will not return to the world of television..

Ziva returns after a six-season absence, and she does so in style, arriving at Gibb's house and declaring, "no time for pleasantries, you're in danger."

So, considering that she left with a bang, how did the writers pull off her reappearance? "It's a hollywood trick," de Pablo told Rachel Ray. "Because there's no body, no crime." As a result, through appearances, she was never really dead.

Why did Michael Weatherly Leave NCIS?

Anthony DiNozzo has been with the NCIS from the beginning, also featuring in the double episode jag feature that launched it, alongside Gibbs and the goth lab genius Abby.

It's career suicide for an actor to remain in one single role for their whole careers though, despite his long experience with the show and the adoring fans.

And, if just for his own sanity, Weatherly wanted a new idea after 13 seasons. Fortunately, the writers obliged, sending Tony an amicable and sentimental send-off that he lived to raise his and Ziva's daughter.

Despite this, he expressed no regrets over leaving the program, saying, "it really felt like a circle that had gone all the way around and i feel really happy with the resolution of character and my time on the show,"

 Despite this, fans can't help but wonder whether we'll ever see special agent DiNozzo again, particularly after Ziva's miraculous reappearance.

So, how possible is it that we'll see DiNozzo again? as the actor said on Entertainment Tonight, "I would never rule anything out..I love NCIS and I certainly love the character of DiNozzo and I miss all my friends over there, particularly the crew."

READ ALSO: Pauley Perette Now 2021: What Does 'Abby' Doing After 'NCIS', 'Broke'? She's Ready for a Tell-All!  

Why did Jennifer Esposito Leave NCIS? 

Since previously becoming involved with blue bloods, this actress potentially had the shortest time on NCIS, having only been a member of the cast for a single season. Her character was a law enforcement training center instructor before being enticed back into the fields by Gibbs, who wants the witty instructor to join his staff.

At first, fans believed she was DiNozzo's successor and were anxious to see what she could add to the program. Unfortunately, this was not the case, and we had to say our goodbyes to the witty agent earlier than we'd hoped.

As fans voiced their dismay at her sudden exit after just one season, Esposito replied by tweeting that her tenure on ncis was never expected to be long."But I'm happy i wasmet some great new friends love to you all,"

"It was  great experience and i could not have asked for a better opportunity than to work with the NCIS cast and producers," the former spin city actress told Deadline of her tenure on NCIS.

Should we hope to see her again if her tenure on the show was so enjoyable?

Alex Quinn left the team to care for her mum, so there's always the chance she'll return, even though the network hasn't confirmed that yet.

Why did Dwayne Henry Leave NCIS?

Season 13 of NCIS welcomed  another new character, Clayton Reeves, played by british actor Dwayne Henry. Sadly, one of the show's creators, Gary Glassberg, who produced Henry's character, died.

Since the writers couldn't know what to do with Reeves, it was determined that he would have to die again. Regardless,

This was a double whammy for viewers, when they not only had to say goodbye to their favorite character, reeves, but also to Abby.

In a tragic season finale, Reeves is murdered by the hitman suspected of killing Abby. So, how did he manage the split? Well, Henry told Looper that he works in a world where you never know what's going to happen, so he's really prepared for something, which includes his murder scene, which he genuinely loved. 

As Henry said, "This is TV history at its finest you can't ask for a better exit like, come on, man." 

So what's next for the man behind the dapper MI6 agent? Many commentators have argued that Henry's lack of roles in major tv shows or films is due to his role on NCIS affecting his career.

However, the actor disagrees, stating that he is taking his time in deciding on his next film.Despite this, he had a minor appearance in the 2019 film Captain Marvel, and we expect to see him again in the near future.

Why did Pauley Perette Leave NCIS?

The face behind the black lipstick, Pauley Perette, will not be returning to NCIS after she left ahead of the show's 16th season. "I believe in God and the world so firmly and it only immediately became blindingly obvious that now was the time after a lot of thinking. I wanted to reveal it myself on Twitter because I didn't want it to be made into something surprising," Perette wrote in a tweet.

Like her coworker Michael Weatherly, it seems that this actress was on the brink of getting bored with the show after 15 years. Even before she made her announcement, the rumor mill went into overdrive, with the media and viewers speculating about whether she left.

This prompted her to post another tweet to clear it up, dispelling rumours about a possible skincare line and vigorously rejecting claims that she returned.

However, the primary explanation for her exit was announced later in 2019. In response to questions about her possible return later in the season, Perete spoke out once more about her tenure on the show.

"I am terrified of harmon and him attacking me" the actress confessed. " I have nightmares about it naturally."

Many fans thought she'd been in an argument with NCIS lead Mark Harmon after seeing this tweet, which was later deleted, which caused uproar.

The fact, though, is no less perplexing. It turns out that Harmon once took his dog to set, only for the canine to viciously strike a crew member, requiring 17 stitches to close.

Perette and the rest of the NCIS staff were rightly alarmed, and Harmon was asked not to bring his dog out.

But for whatever reason, he didn't listen, and as a result, Pauley Perrette felt so uneasy around Harmon and the dog that they began shooting their scenes separately.

But how did she feel about leaving? According to Cinema Blend, Perette took the break pretty hard, writing, "It makes me sad to imagine a world without Bbby in it. It really makes me sad. i'm still grieving."

So who's the next to pack their bags of the original NCIS cast?

Read More: Why Did Abby Leave NCIS? Pauley Perette's Disdain Over Mark Harmon Reportedly Reaches Beyond His Dog