How I Met Your Mother had a major tradition of featuring previous cast members of Buffy the Vampire Slayer. Although the shows didn't share the same network or creative figures behind the camera, many Sunnydale residents made their way to the Big Apple for the NBC sitcom. How I Met Your Mother debuted two years after Buffy accomplished a seven-season run split between The WB and UPN.
Buffy the Vampire Slayer was created by Joss Whedon and starred Sarah Michelle Gellar as a young "Slayer" from Sunnydale called upon to face off against the likes of vampires, demons, and other supernatural forces. The series, which debuted in 1997, introduced many core characters that teamed up together to form the Scooby Gang. In addition, there were many faces that made recurring and guest appearances. After the success of Buffy, the series launched a spinoff including books, comics, and video games.
Despite ending in the early '00s, Buffy became a cult classic series. The creators of How I Met Your Mother, Carter Bays and Craig Thomas, were major fans, explaining why they sought after many Buffy vets to appear in their sitcom. Not only did they feature Buffy actors but they also cast members from Whedon's other projects. Buffy was arguably the most popular title and here's every actor from the series that later appeared in How I Met Your Mother.
Alyson Hannigan
Alyson Hannigan was the most prominent cast member in How I Met Your Mother to previously star in Buffy the Vampire Slayer. She played Willow Rosenberg, a close friend of Buffy Summers and a member of the core set of friends, for the duration of the supernatural series. A family member of co-creator Craig Thomas was a Buffy fan and suggested the actress for the role of Lily Aldrin in How I Met Your Mother. She wound up playing the character for nearly a decade.
Alexis Denisof
Alyson Hannigan's husband, Alexis Denisof, memorably played Sandy Rivers in How I Met Your Mother. The anchor of Metro News One and former coworker of Robin appeared in 10 episodes throughout the sitcom. Before appearing in the comedy, Denisof spent time on Buffy as Wesley Wyndam-Pryce, a member of the Watchers' Council before moving to the spinoff, Angel, as a main character.
Kal Penn
Kal Penn played the recurring character, Kevin Venkataraghavan, in How I Met Your Mother. Kevin was the therapist of Robin before the duo entered a short-term relationship. Penn actually played two different characters in Buffy including a UC Sunnydale student named Hunt and a humanoid demon referred to as "John Hancock."
Harry Groener
In Buffy, Harry Groener portrayed Richard Wilkins, the mayor of Sunnydale who was a sorcerer with aspirations of becoming a pure-blood demon. The actor played a much different character in How I Met Your Mother by playing the recurring role of Clint, the second husband of Ted's mother, Virginia. Clint had a laid back personality that seemed to bother Ted, especially when it came to his hippie-like views on life.
Rachel Bilson
Before appearing on The O.C., Rachel Bilson had an appearance on Buffy as Colleen, a "Potential Slayer" from season 7. The actress later moved on to How I Met Your Mother as Casey, an ex-girlfriend of Ted who later went on to marry a woman. It was also revealed that Cindy was once a roommate of Tracy, the future wife of Ted.
Other Buffy The Vampire Slayer Alums In Minor HIMYM Roles
Ian Abercrombie: The Ben Franklin actor in How I Met Your Mother also played a Techno-Hunter a season 3 episode of Buffy the Vampire Slayer.
Nancy Lenehan: The actress played the role of Pat in an episode of Buffy before taking took over the role of Cheryl Whittaker, Barney's stepmom, in How I Met Your Mother.
Tom Lenk: After playing two different characters, Cyrus and Andrew Wells, in Buffy, Lenk played Scott the Barista in the "Swarley" episode of How I Met Your Mother.
Danny Strong: Prior to playing the minister at Marvin Eriksen's funeral, Strong played the Buffy character, Jonathon Levinson, a warlock and member of the Trio.
Seth Green: The actor played the prominent role of Daniel "Oz" Osbourne, the werewolf and member of the Scooby Gang, in Buffy and had a cameo as Daryl LaCouture in How I Met Your Mother season 8.
Caroline Lagerfelt: Before appearing as a woman in the bridal shop in an episode of How I Met Your Mother, Lagerfelt portrayed Spike's mother, Anne Pratt, in Buffy.
Pat Crawford Brown: Thelma, the lady that Lily met on the plane in How I Met Your Mother season 4 was the same actress who played the creepy old woman the "Doublemeat Palace" episode of Buffy.
Phil Lewis: The actor who portrayed Mr. Platt, a guidance counselor at Sunnydale High also played a loan officer in How I Met Your Mother season 3.
Adam Paul: After playing the "Skanky Vampire" in an episode of Buffy the Vampire Slayer, Paul joined How I Met Your Mother to play Mitch, the inventor of "The Naked Man."