NCIS season 22 premiering in October, NCIS stands as one of the longest-running scripted series, a feat attributed to its dedication to character integrity. The franchise has honed various strategies to navigate significant casting fluctuations, all rooted in a steadfast rule protecting character continuity.

NCIS is a series built on rules and values. Mark Harmon's Leroy Jethro Gibbs, famously lived by a set of rules, a legacy from his wife, Shannon. The young Shannon Gibbs character revealed her own code in a flashback in "Heartland," which is one of the NCIS. The series' success calls to mind Gibbs' Rule #34: There is no such thing as a coincidence. The series' longevity on CBS can be traced back to the meticulous maintenance of one rule: never recast a character.

NCIS Has Never Recast A Major Character In 21 Years

NCIS Would Rather Kill Its Characters (& That's A Good Thing)

Since the series began in 2003, NCIS has never recast a major character in 21 years. Instead, when an actor leaves the series, the police procedural writes the character out and moves on. This tactic is the key to the series' success because it more accurately depicts the nature of life: sometimes, people die, relocate, or take a different job, and people need to move on without them. Inversely, it's disorienting when television replaces a familiar character with a different actor. People come and go from a life but rarely change their persona and core physical characteristics.

Major NCIS characters who have been written out of the series include Kate Todd, Ziva David, Tony DiNozzo, Eleanor Bishop, and Leroy Jethro Gibbs.

While it's understandable that series sometimes recast a character, NCIS would rather send its characters off, creating a more complex narrative while maintaining continuity. For instance, after Sasha Alexander left NCIS after just two seasons, her character, Caitlin Todd, was shot in the head and skillfully replaced with Cote de Pablo's Ziva David. Kate's shocking death signaled to audiences that no character was safe. It intensified the lengths the series was willing to reach to tell captivating stories, and the change only added to the series' success; Ziva was one of the most beloved NCIS characters ever.

Why Recasting Main Cast Is Tricky In NCIS

NCIS Characters Are Irreplaceable

Even if the series did want to recast its characters, it would be tricky. Many NCIS characters stay with the series for decades, which complicates someone else stepping into the role and making it their own. Recasting Gibbs was unthinkable when the series had to navigate Mark Harmon's NCIS exit. Harmon helped establish NCIS as Gibbs, and no one else could fill his role since he was quintessential to the franchise. Instead, the series brought in Gary Cole's Alden Parker character – an FBI agent who had nothing in common with Gibbs but is memorably tied to his departure.

NCIS season 22 and NCIS: Origins premiere on CBS on Monday, October 14.

The exception to this rule has been recasting characters from Gibbs' past. The character itself was recast for NCIS: Origins — an inevitability, considering the show's prequel nature. While Sean Harmon technically could have resumed his role as young Gibbs, the actor never had a significant role in the original series, so it makes sense that the series took a casting risk with NCIS: Origins. Beyond that, however, NCIS has maintained an impressive streak by not recasting any major character from the flagship project.