While television has created some huge stars, the fact remains that most TV actors are expendable. The main cast of beloved series such as Friends, The Big Bang Theory, and Game of Thrones have been able to command huge salaries on back of those shows' massive popularity, and executives are clearly happy to pay them. But actors are rarely more important than the series itself, and stars are usually written out of a show when they decide to leave (or are fired).

But while a main character might simply be killed off or moved out of town once an actor leaves the role, there's an even easier solution for smaller roles and supporting cast members--simply change the actor. The producers of Friends weren't about to recast, say, Ross, but switching the actor who played his ex-wife was no problem. Similarly, characters played by younger children frequently have to be recast when the kids grow up, go to school, or simply leave the profession.

Actor switches happen all the time, and many go unnoticed by viewers. But there have been some bigger ones over the years. Some of these were smaller roles in huge shows, and some surprisingly big switches that were unavoidable to keep the series going. And some were totally deliberate recastings. So here are 11 key actor changes that have taken place over the years...

11. Alura Zor-El in Supergirl

Kara's Kryptonian mother Alura Zor-El was played by Laura Benanti in the first two seasons of Supergirl, but filming commitments elsewhere meant she couldn't return for Season 3. But her replacement was a familiar name to DC fans--Erica Durance, who played Lois Lane in Smallville.

10. Helene Beesly in The Office

Pam's mom Helene first appeared in The Office Season 2, played by Shannon Cochran, in the episode "Sexual Harassment." The character didn't appear again until Season 6, when she had been replaced by Linda Purl. From that point, Helene became a more regular character, appearing in five episodes in Season 6 and 7.

9. Carol Willick in Friends

When an actor is switched after just one episode, it's usually easy to forget that there was ever a change. But when that show is as endlessly rewatched and discussed as Friends, then even the smallest inconsistency is hard to ignore. Ross's ex-wife Carol was played by Anita Barone in Episode 2 of Friends back in 1994. By Carol's next appearance, seven episodes later, she had been replaced by Jane Sibbett, who continued to play her throughout the next decade of the classic show.

8. The Mountain in Game of Thrones

Game of Thrones had two notable recastings throughout its 10-year-run. Gregor Clegane--aka The Mountain--was played by three different actors. Conan Stevens appeared as the character in Season 1, with Ian Whyte taking over for Season 2. The role was recast yet again for Season 3, with Hafþór Júlíus Björnsson playing The Mountain all the way through to his death at the Battle of King's Landing in Season 8.

7. Morgan Matthews in Boy Meets World

The casting of children in shows that could potentially span many years is always problematic--sometimes, the characters need to age faster or slower than the kids in real life, and sometimes, it's simply a matter of real life getting in the way. In Boy Meets World, young Morgan Matthews was played by Lily Nicksay for 35 episodes, before being replaced in 1993 by Lindsay Ridgeway. According to co-star Rider Strong, Nicksay, who was only 7 when she left, simply didn't enjoy making the show. Nicksay did however return to reprise the role two decades later, in the 2017 series finale of spin-off Girl Meets world, appearing alongside Ridgeway for a very meta in-joke.

6. James Kent in True Blood

The smart and sensitive vampire James Kent was introduced into True Blood in Season 6, played by Luke Grimes. But within a season, he had been recast, with Nathan Parsons taking over for the final Season 7. The official reason from HBO at the time was because of "the creative direction of the character." But a subsequent report in Buzzfeed stated that it was because Grimes was uncomfortable playing a gay character, and the show's producers were unwilling to rewrite the scripts to accomodate him.

5. Daario Naharis in Game of Thrones

Daario was another recast character in Game of Thrones. He was played initially by Ed Skrein for three episodes in Season 1, but when the character returned in Season 4, Skrein had been replaced by Michiel Huisman. At the time, it was reported that Skrein left to focus on his movie career, but he subsequently denied this was the case. "My plan was to stay with Game of Thrones for the long haul," he told Entertainment Weekly. "That was always my plan. It was a wonderful experience, but politics led to us parting ways."

4. Most of the cast in Last Man Standing

There are few shows that have had quite so many dizzying recastings as the Tim Allen family sitcom Last Man Standing. Some characters, such as Kristin Baxter, were recast after a single season (Alexandra Krosney to Amanda Fuller), while others, like sister Mandy, made it through six seasons before getting a new actor (Molly Ephraim to Molly McCook). Younger brother Boyd has been played by four different actors (Evan and Luke Kruntchev, Flyn Morrison, Jet Jurgensmeyer), while Nick Jonas' guest role in season 1 was recast for Season 2 when his character became a regular. And if all that wasn't confusing enough, one actor was given two completely separate roles--Jonathan Taylor Thomas played restaurant boss John Baker in Season 2 and 3, and then returned for Season 4 as a new character named Randy, which was the name of his Home Improvement character.

3. Ann Veal in Arrested Development

Arrested Development was a very self-referential show--how many series would make repeated jokes about its own impending cancelation? The recasting of George Michael's very forgettable girlfriend Ann after one episode, from Alessandra Torresani to Mae Whitman, was in fact part of the joke that none of the characters could really remember her any time they met. In fact, the original plan was to keep the gag going and recast the role for every single episode she appeared in. But Whitman was so good at playing the boring, bland Ann that she was kept on for the next three seasons.

2. Bobby Draper in Mad Men

Another prominent swap of child actors was in Mad Men, where Don Draper's son Bobby was played by no fewer than four youngsters across its seven seasons. In order, they were: Maxwell Huxabee, Aaron Hart, Jared S. Gilmore, and Mason Vale Cotton. However, Kiernan Shipka, who played Bobby's older sister Sally throughout the whole show, subsequently revealed that there were also some "unofficial" Bobbys who appeared briefly in specific scenes, including "Bucket Head Bobby" and "Slurpee Bobby."

1. Becky Conner in Roseanne

The initial cast switch for Becky Conner might have been done through necessity, but as the years went on, producers came to embrace having two actors in the role. Lecy Goranson played Becky in Roseanne's first four seasons, but left the show in 1993 to attend college. Sarah Chalke replaced her, and played Becky throughout Seasons 5, 6, and 7. With Season 8 expected to be the final one, the bold decision was made to have both actors play the role--Goranson would appear when her school schedule allowed, with Chalke covering for her at other times. But the confusion didn't stop there. When Roseanne was renewed for its controversial ninth and final season, Chalke took on the role full-time again. And when the series made its short-lived return in 2018, Goranson was back, but with Chalke rejoining the show in a new role--Andrea, a surrogate mom hired by Becky. Phew! On the current iteration of the series, the Roseanne-free The Conners--Goranson continues to portray the role of Becky.