TV Shows That Turned One-Off Guest Stars Into Series Regulars

Television production is a fluid process where writers often adjust storylines based on actor chemistry and audience reception. Many iconic characters were originally written as temporary additions or single-episode appearances intended to create brief conflict. These actors impressed producers so thoroughly that their roles were expanded into central figures of the series. The following shows demonstrate how a planned cameo can evolve into a legendary television legacy.

‘Family Matters’ (1989–1998)

Jaleel White was originally cast for a single episode to play the annoying neighbor Steve Urkel. The audience reaction during the taping was so overwhelming that producers immediately sought to bring him back. Urkel rapidly transformed from a one-off nuisance into the primary focus of the entire series. His catchphrases and physical comedy overshadowed the original premise of the show centered on the Winslow family. This casting change completely altered the tone and longevity of the sitcom.

‘Parks and Recreation’ (2009–2015)

Chris Pratt was initially contracted to appear as Andy Dwyer for only six episodes in the first season. Writers planned for him to be the lazy boyfriend that Ann Perkins dumps before moving on with her life. The creators found Pratt so naturally funny and charming that they decided to keep him as a permanent resident of Pawnee. Andy went on to become a lovable series regular who eventually married April Ludgate. His character arc became one of the most heartwarming aspects of the show.

‘Lost’ (2004–2010)

Michael Emerson was cast to play Henry Gale for a three-episode arc in the second season. His portrayal of the manipulative and ambiguous prisoner impressed the showrunners enough to rewrite their long-term plans. The character was revealed to be Ben Linus and became the primary antagonist and later an uneasy ally for the survivors. Emerson remained a pivotal part of the ensemble through the series finale. His performance earned him widespread critical acclaim and multiple award nominations.

‘Justified’ (2010–2015)

Walton Goggins played Boyd Crowder in the pilot episode with the script calling for his death at the end of the hour. Test audiences responded positively to the magnetic chemistry between Goggins and lead actor Timothy Olyphant. Producer Graham Yost decided to keep the character alive and elevated him to the main antagonist. Boyd Crowder became the perfect foil to Raylan Givens throughout the entire run of the series. This decision added layers of complexity to the show that would have been missing otherwise.

‘The West Wing’ (1999–2006)

Martin Sheen was originally signed to appear in only four episodes per season as President Josiah Bartlet. The series was designed to focus on the senior staff members rather than the President himself. Sheen commanded such a powerful presence in the pilot that the producers realized the show needed him as a central anchor. He was upgraded to a main cast member immediately and appeared in every episode of the first season. The show subsequently revolved heavily around his presidency and personal life.

‘Stranger Things’ (2016–Present)

Joe Keery played Steve Harrington as a stereotypical high school bully who was slated to die in the first season. The Duffer Brothers enjoyed Keery’s likability and decided to give his character a redemption arc instead. Steve evolved from an antagonist into a protective babysitter figure for the younger group of kids. His partnership with Dustin Henderson became a fan-favorite element of the series. This shift allowed the show to explore more complex character growth than originally anticipated.

‘Arrow’ (2012–2020)

Emily Bett Rickards was hired for a one-scene role as an IT technician named Felicity Smoak. Her chemistry with star Stephen Amell was instantly apparent to the producers and the network executives. They expanded her role into a recurring character before making her a series regular in the second season. Felicity became an essential member of Team Arrow and the primary love interest for Oliver Queen. Her inclusion brought a necessary lightness and humor to the otherwise gritty superhero drama.

‘Supernatural’ (2005–2020)

Misha Collins joined the show in season four as the angel Castiel for a limited six-episode story arc. The introduction of angels introduced a new mythology that revitalized the series and fans latched onto the character immediately. Collins was eventually promoted to a series regular and became the third lead alongside the Winchester brothers. Castiel remained a core part of the show for over a decade until its conclusion. His character provided a crucial supernatural ally for Sam and Dean.

‘Buffy the Vampire Slayer’ (1997–2003)

James Marsters was cast as the vampire Spike for a brief villainous arc that was supposed to end with his death. The character proved to be incredibly popular with fans due to his punk rock aesthetic and snarky attitude. Joss Whedon decided to keep Spike alive and he eventually transitioned from a villain to a reluctant hero. He became a series regular and a romantic interest for Buffy in later seasons. Marsters even carried the character over to the spinoff series ‘Angel’ after ‘Buffy’ ended.

‘The Office’ (2005–2013)

Ed Helms joined the cast in the third season as Andy Bernard for a temporary arc involving the Stamford branch merger. The writers originally planned to have his character leave the show when the branches combined or shortly thereafter. Helms integrated so well with the ensemble that he was kept on as a permanent employee of Dunder Mifflin. Andy eventually rose to become the Regional Manager in later seasons. His musical talents and anger management issues provided ample comedic material for the show.

‘Law & Order: Special Victims Unit’ (1999–Present)

Ice-T was originally brought in to play Detective Fin Tutuola for a four-episode arc to cover for another actor. The chemistry between him and Richard Belzer was so strong that creator Dick Wolf offered him a permanent spot on the squad. Fin became a staple of the series and eventually rose to the rank of Sergeant. He is now the second longest-serving character in the history of the franchise. His unique perspective and street smarts became essential to the dynamic of the SVU team.

‘The Good Wife’ (2009–2016)

Alan Cumming appeared as campaign strategist Eli Gold for what was intended to be a short guest arc. The character was only supposed to help Peter Florrick through a portion of his campaign. Critics and audiences praised Cumming’s performance and the energy he brought to the political storylines. He was promoted to a series regular in the second season and stayed until the finale. Eli Gold became one of the most complex and entertaining characters in the legal drama.

‘Scrubs’ (2001–2010)

Neil Flynn was cast as the Janitor for the pilot episode as a figment of the main character’s imagination. The creator intended to reveal at the end of the first season that only J.D. could see him. Flynn was so funny during filming that the writers abandoned this twist and made him a real person interacting with the whole staff. The Janitor became the primary antagonist for J.D. and a series regular. His improvisational skills added a unique layer of absurdity to the hospital comedy.

‘Cheers’ (1982–1993)

Kelsey Grammer was introduced as Dr. Frasier Crane for a few episodes as a romantic rival to Sam Malone. The producers planned to write him out after his relationship with Diane Chambers ended. Grammer’s performance was so compelling that the writers found ways to keep him in the bar as a regular patron. Frasier became a central member of the ensemble for nearly a decade. The character was successful enough to spawn his own spinoff series that ran for another eleven seasons.

‘Shameless’ (2011–2021)

Noel Fisher played Mickey Milkovich as a recurring neighborhood thug and antagonist in the first season. His complicated relationship with Ian Gallagher resonated deeply with the audience and the writers. Fisher was eventually promoted to a series regular as his character underwent significant development. Mickey evolved from a violent criminal into a loving husband and one of the show’s most beloved figures. His journey of self-acceptance became a defining narrative of the series.

‘The Big Bang Theory’ (2007–2019)

Melissa Rauch appeared as Bernadette Rostenkowski in the third season as a short-term love interest for Howard. The writers originally did not intend for the relationship to last beyond a few episodes. Her distinct voice and ability to keep Howard in check made her a valuable addition to the group dynamic. She was promoted to the main cast in season four alongside Mayim Bialik. Bernadette became a central character who balanced her career in microbiology with family life.

‘Community’ (2009–2015)

Jim Rash was initially a recurring guest star as Dean Pelton during the first two seasons of the show. His eccentric entrances and costumes became a highlight of every episode he appeared in. The producers recognized his comedic value and promoted him to the main cast for the third season. Dean Pelton became an integral part of the study group’s adventures rather than just an administrator. His obsession with Jeff Winger provided a running gag that lasted throughout the series.

‘Happy Days’ (1974–1984)

Henry Winkler was cast as Arthur Fonzarelli in a secondary role with very few lines in the early episodes. The network executives wanted to limit his screen time because they feared his leather jacket image was too aggressive. Fonzie became an overnight sensation and his popularity quickly eclipsed the other characters. He was moved to center stage and became the face of the show for the rest of its run. The character remains one of the most recognizable figures in television history.

‘Glee’ (2009–2015)

Naya Rivera was cast as Santana Lopez strictly to fill out the background numbers in the glee club. She had very few lines in the first season and was essentially a background antagonist. The writers noticed her sharp comedic timing and vocal talent which led to a significantly expanded role. Santana became a main character in the second season with major storylines focused on her sexuality and ambition. Her character arc became one of the most critically acclaimed aspects of the musical dramedy.

‘Once Upon a Time’ (2011–2018)

Colin O’Donoghue was cast as Captain Hook for a recurring arc in the second season of the fantasy drama. The character was designed to be a villain who would create trouble for the heroes before being defeated. Fan reaction to his charismatic portrayal was immediate and positive. The writers pivoted his storyline to a redemption arc and he became a romantic lead for the protagonist Emma Swan. Hook remained a central hero and series regular until the show concluded.

Tell us which of these character transformations surprised you the most in the comments.