Change is inevitable even on hit TV series.
Sometimes actors get bored or leave for personal reasons.
Other times, producers and writers get tired of actors and find a ratings-grabbing manner in which to get rid of them.
Some series, such as M*A*S*H or Grey's Anatomy or Law & Order, make cast changes seamlessly seemingly for decades.
Still, an essential actor can leave and his or her character gets written out, and the series falls apart. Everyone has one of those (how could Sleepy Hollow have continued without Abbie?).
Sure, many shows shuffle their lineups in their first or second seasons, until they find their mojo. Does anyone remember Agent Vivian Blackadder (great name for a BBC character) on the JAG episodes which introduced NCIS?
The photos below look at good and bad transitions on long-running network series.
Comment below with your best and worst casting changes.
Chin and Kono - Hawaii Five-0
With its original lineup, Hawaii Five-0 had more of a family feel. That started with protective Chin and his younger cousin, Kono. He, McGarrett and Danny were bickering brothers, and Kono the younger sister. But things had to evolve with the contract-driven departures of Daniel Dae Kim and Grace Park.
Tani and Junior - Hawaii Five-0
The departures of Chin and Kono for jobs on the mainland left the Five-0 task force short-handed. Enter Tani, a Police Academy dropout, and Junior, like McGarrett a former Navy SEAL. Unlike their predecessors, they're rookies learning from scratch. They seem like work buddies now, but might they be something more in the future?
Hetty Lange - NCIS: Los Angeles
Then there's the wrong way to handle changes. For eight seasons, Hetty has been the best of the NCIS directors. She's like one of those Russian nesting dolls, the little doll inside wrapped in layers of secrets. She's been the Yoda for the Los Angeles unit. But she's spent NCIS: Los Angeles Season 9 trapped in Vietnam. Whether that's Linda Hunt's choice or the writers' idea, it's hurt the series.
Shay Mosley - NCIS: Los Angeles
That's because Hetty has been replaced, hopefully temporary, by Mosley, a caricature of the heartless bureaucrat. She's come to Los Angeles to correct all the agents' bad habits. All that's needed is the Wicked Witch theme and some flying monkeys whenever she comes on screen. There's been some feeble attempts to humanize her, which have failed. I feel badly for Hidoko, who is seen as guilty by association. Time to rescue Hetty!
Jason Gideon - Criminal Minds
Gideon set the tone for this series about the profilers of the Behaviorial Analysis Unit. Rejoining the unit after medical leave for PTSD, he was always on edge and could too easily get into the mindset of the unsubs they hunted. When Mandy Patinkin left after two seasons, later saying it was destructive to his soul, it was easy to sell Gideon departing because of emotional issues caused by his girlfriend's death.
David Rossi - Criminal Minds
When the time came to replace Gideon, who better than Rossi, his former partner and best friend? Rossi came back from early retirement, leaving behind lecture and book tours to take care of unspecified unfinished business. While Rossi has his demons, he just doesn't seem as tightly wound as Gideon. He has a life outside the BAU, and seems like everyone's fun uncle.
Merri Brody - NCIS: New Orleans
Brody, we hardly knew ye. For two seasons. Brody served with Dwayne Pride's team, without a whole lot of character development. Then she got romantically involved with the wrong guy and quit before NCIS: New Orleans: Season 3. Why? One rumor is that Zoe McLellan left the series for personal reasons. Another was that Brody was written out for creative reasons. Make your own guess.
Tammy Gregorio - NCIS: New Orleans
Brody's sudden exit left an opening which was filled by Gregorio. Following Brody's Midwestern sweetness, Gregorio's New Yawk attitude has been a tough sell. Fortunately, the former FBI agent received a well-developed back story, and she's softened over the past two seasons. Now what happens when Shalita Grant's Percy leaves after this season? Fortunately, Christopher LaSalle is a constant.
Lance Sweets - Bones
The cerebral Lance Sweets earned his place among the FBI/Jeffersonian crew, despite skepticism from both Brennan and Booth. Fans also enjoyed his on-again, off-again relationship with "squintern" Daisy. But after nine seasons, John Francis Daley's burgeoning directing career led to Sweets being killed off the series.
James Aubry - Bones
Sweets' death left an opening for a new sidekick for Booth for the series' final four seasons. Like Sweets, Aubrey also became involved with a "squintern." He also got derided for his horrible eating habits. Later in the run, it was revealed that Aubrey's father was a fugitive white-collar criminal. Aubrey wasn't an offensive character. He just wasn't Sweets.
Gil Grissom - CSI
For nine seasons, Gil Grissom was the quirky voice of wisdom for the Las Vegas CSI unit. Grissom provided the vibe for the series, and made science geekiness cool, as forensics programs popped up all over the country. When William Peterson left to take on other roles, it set the cast carousel in motion on the venerable procedural.
D.B. Russell - CSI
D.B Russell became the graveyard shift supervisor at the start of CSI Season 12 and stayed for the final four seasons. He even jumped over to CSI: Cyber Season 2, the final gasp of the franchise. You can never go wrong casting Ted Danson (with Becker the notable exception). His Russell was a calm space in a crazy world, that of Las Vegas after dark.
Ziva David - NCIS
No, not DiNozzo. There's no replacing Tony, even with multiple new agents, as NCIS has found out. No, I'm looking at Ziva, the female lead for this long-running series. For 11 years, she was the action hero NCIS needed, and viewers loved her sexual tension with DiNozzo. They should have paid her what she wanted. And they shouldn't have killed her off just to ease Tony's exit.
Emily Bishop - NCIS
(See what I mean about DiNozzo?) Poor Emily Bishop. Ziva is a damn hard act to follow. But Bishop was written in smartly, starting as an NSA analyst and slowly finding her way as a field agent. She's had a rough go of it, with a cheating husband and an assassinated boyfriend. But Bishop has spunk. I like spunk. She's also fit smoothly into the team which NCIS has become.
Elliot Stabler - Law & Order: SVU
For 12 seasons, Stabler was half of the winning formula that was SVU. He was a rock, seeking justice for victims, regardless of what it cost him in his personal life. And then he was suddenly gone, supposedly because of guilt over a squadroom shooting. The truth is that contract negotiations fell apart with Christopher Meloni, and series executives decided to go a different route.
Olivia Benson - Law & Order: SVU
The focus shifted to the remaining half of the winning formula. It's all about Benson now: her dedication, her loves, her son. She eventually became captain and is aided by Finn and a changing squad around her. As long as the cases stay engrossing and ripped from the headlines, Olivia and SVU will successfully soldier on. Barba leaving hurts, though.