Jesse Pinkman, Breaking Bad
If it weren't for the crazy good chemistry between Aaron Paul and Bryan Cranston, Breaking Bad would have been a very different show. Creator Vince Gilligan was originally planning to kill Jesse off in the first season until he took a look at his two main actors and made the decision to not only keep Jesse around, but make the show more about the dynamic between the two men. Paul went on to win 2 Supporting Actor Emmys, and is even nominated one last time in 2014.
Sue Sylvester, Glee
The infamous Sue Sylvester was almost not the star she is today! When the show first started, Jane Lynch was attached to a Damon Wayans pilot on ABC, and couldn't commit to being more than just a recurring character. When that pilot wasn't picked up, Lynch went to work at McKinley High full time, and we will never look at a tracksuit the same way again.
Mark Rollins/etc, Orphan Black
After it was revealed that he was one of the male clones of Project Castor in the season 2 finale Orphan Black, it's sort of ridiculous to think that Mark was slated to die after just six episodes. Co-Creator John Fawcett explained that Ari Millen was just too good to kill off. "He just blew our minds over and over with all of these great scenes, and we just saw all this great potential in that character," Fawcett told us, "It really wasn't too much later that we decided to definitely not kill him and in fact use him as the male clone that we introduced."
Dylan McKay, Beverly Hills 90210
Fox executives were so not sold on Luke Perry or the character that not only would they only cast him for one or two episodes, but Aaron Spelling had to pay Perry's salary for those episodes out of his own pocket. Of course, the execs wised up pretty quickly after they saw the audience response, so Perry became a regular cast member, and the rest is history.
Jack Shephard, Lost
Can you imagine Lost without Jack (or Matthew Fox)? Originally, the part was supposed to be played by Michael Keaton and Jack was supposed to be killed by the monster in the pilot, leaving Kate (Evangeline Lilly) as the leader of the survivors. However, ABC executives managed to convince the creators that killing off the likable main character in the first episode would generate feelings of betrayal and anger among audience members. (Duh.) The writers compromised by writing in and then killing off Oceanic Flight 815's pilot, instead, and we are forever grateful.
Captain Hook, Once Upon a Time
It's hard to imagine OUAT without its Captain Hook, right? Well, according to the pirate himself, he was only supposed to be making a temporary trip to Storybrooke. "I came in on episode four of the second season and I just thought I was going to be a guest star for a couple of episodes and here I am still!" O'Donohgue recently told us. "It's probably the eyeliner to be honest. I think that's the winning formula that's kept me on the show."
Luke Danes, Gilmore Girls
The curmudgeonly yet lovable Luke was saved from a post-pilot disappearance by Scott Patterson's fantastic chemistry with Lauren Graham, and our fragile hearts were saved from never knowing the beauty of true caffeine-fueled love.
Sophia Petrillo, The Golden Girls
The Golden Girls without Estelle Getty? It was almost a reality, as Sophia was only meant to appear in the pilot until she was so popular with the viewers that she ended up sticking around.
Andy Bernard, The Office
Did we like Andy? Did we hate him? We never did figure that out, but at least we had time to try! Ed Helms was originally signed on for only 10 episodes, but his personality matched so perfectly with the character that the writers had in mind that they brought him back as a regular, and an integral part of the show.
Ben Linus, Lost
Michael Emerson was originally just cast for a guest-starring role because the producers of Lost liked his work on The Practice, but as we all know, things didn't turn out as planned. Ben Linus became one of the most compelling characters on television, and Emerson went on to win an Emmy for his work on the show's fifth season.
Mimi Bobeck, The Drew Carey Show
Another show, another character originally intended to only appear in the pilot. Mimi (Kathy Kinney) was just a woman in bad make up applying for a job in a make up department, and she became Drew Carey's greatest frenemy thanks to her popularity with viewers.
Summer Roberts, The O.C.
Seth Cohen's eventual wife could have just been a small part in a few episodes, designed as the stereotypical mean girl BFF to Marissa. Instead, the character, played by Rachel Bilson, was a hit and took over as the show's leading lady after Marissa's death in season three. So not ew!
Spike, Buffy the Vampires Slayer
Buffy herself may be Team Angel, but we're Team Spike (James Marsters) all the way. He was intended to be just another one-off villain for Buffy to defeat, but ended up being one of the most fully-developed characters on the show. He got to be bad, he got to be good, and he got to be everywhere in between. He also got to save the world and then joined Angel as a vampire ghost!
Topanga Lawrence, Boy Meets World
What would Cory have done without Topanga? Luckily, we never had to find out, even though Danielle Fishel was only hired for the small role of an off-kilter middle school hippie. As she became more important to the show, she also became a lot smarter and a lot less weird, and one of television's greatest teen relationships, and an eventual hit spinoff series in Disney Channel's Girl Meets World, was born.
Jed Bartlet, The West Wing
Aaron Sorkin's original plan for The West Wing was sort of a Veep situation where the POTUS is never actually seen. He worried that would be a little too gimmicky, and started considering actors for a recurring role. Martin Sheen originally signed on for four episodes, but his acting was so impressive that producers asked him to join the regular cast, and thus began one of the greatest fictional Democratic presidencies in recent memory.
Steve Urkel, Family Matters
If you can believe it, Steve Urkel (Jaleel White) was only supposed to be one season one episode of Family Matters as a nerdy guy who takes Laura on a date. The character was so popular with the studio and home audiences that he was brought back for more and more episodes before the show became all about Urkel. The character was even named after the real-life friend of co-creator Michael Warren, who sort of regretted dooming his friend to years of prank calls and side-eye when Urkel turned into more than just a one-episode guest star.
Lafayette Reynolds, True Blood
Arguably one of True Blood's best characters, Lafayette (Nelsan Ellis) only makes it through one of the books the show is loosely based on before Sookie finds him dead in the back of Andy's car. Diverging from the book made complete sense, since Lafayette is awesome, but we think it still might have been entertaining to watch Sookie discover that Lafayette was (spoiler!) killed by the members of Bon Temps' secret sex club after an orgy gone wrong.
Frasier Crane, Cheers
Kelsey Grammer was hired for six episodes of Cheers, and went on to play the character of Dr. Frasier Crane for a full 20 years on two incredibly successful shows. That run is tied with James Arness of Gunsmoke, and the only other TV actor to have played a character longer than that is Richard Belzer, who played Detective John Munch in the Law & Order franchise.
Boyd Crowder, Justified
The strangely lovable career criminal, played by Walton Goggins, wasn't even supposed to make it past the first episode, since he was just appearing on the show as a favor to his friend, Timothy Olyphant. After he was shot in the pilot, that should have been the end of him. However, test audiences liked the character, so he was brought back and he eventually became a main character. We wouldn't have it any other way.